Split documents per OS, fix few things, drop and add few OSes (#5328)

* Exclude include files from being built

* Split install guides into multiple documents (one per OS/version combo)

* Update references

* Unify anchor names

* Update pyenv requirements in CentOS 7 guide

* Update install guides for RHEL derivatives to not use pyenv

* Add guide for Rocky Linux 8

* 8.4+ -> 8.4-8.x

* Add 'the'

docs/install_guides/_includes/create-env-with-pyenv-virtualenv.rst

@@ -0,0 +1,44 @@
+------------------------------
+Creating a Virtual Environment
+------------------------------
+
+.. tip::
+
+    If you want to learn more about virtual environments, see page: `about-venvs`
+
+We require installing Red into a virtual environment. Don't be scared, it's very
+straightforward.
+
+**************************
+Using ``pyenv virtualenv``
+**************************
+
+Using ``pyenv virtualenv`` saves you the headache of remembering where you installed your virtual
+environments. This option is only available if you installed Python with pyenv.
+
+First, ensure your pyenv interpreter is set to python 3.8.1 or greater with the following command:
+
+.. prompt:: bash
+
+    pyenv version
+
+Now, create a virtual environment with the following command:
+
+.. prompt:: bash
+
+    pyenv virtualenv <name>
+
+Replace ``<name>`` with whatever you like. If you ever forget what you named it,
+you can always use the command ``pyenv versions`` to list all virtual environments.
+
+Now activate your virtualenv with the following command:
+
+.. prompt:: bash
+
+    pyenv shell <name>
+
+.. important::
+
+    You must activate the virtual environment with the above command every time you open a new
+    shell to run, install or update Red. You can check out other commands like ``pyenv local`` and
+    ``pyenv global`` if you wish to keep the virtualenv activated all the time.

docs/install_guides/_includes/create-env-with-venv.rst

@@ -0,0 +1,38 @@
+------------------------------
+Creating a Virtual Environment
+------------------------------
+
+.. tip::
+
+    If you want to learn more about virtual environments, see page: `about-venvs`
+
+We require installing Red into a virtual environment. Don't be scared, it's very
+straightforward.
+
+**************
+Using ``venv``
+**************
+
+This is the quickest way to get your virtual environment up and running, as `venv` is shipped with
+python.
+
+First, choose a directory where you would like to create your virtual environment. It's a good idea
+to keep it in a location which is easy to type out the path to. From now, we'll call it
+``redenv`` and it will be located in your home directory.
+
+Create your virtual environment with the following command:
+
+.. prompt:: bash
+
+    python3.9 -m venv ~/redenv
+
+And activate it with the following command:
+
+.. prompt:: bash
+
+    source ~/redenv/bin/activate
+
+.. important::
+
+    You must activate the virtual environment with the above command every time you open a new
+    shell to run, install or update Red.

docs/install_guides/_includes/install-and-setup-red-unix.rst

@@ -0,0 +1,56 @@
+--------------
+Installing Red
+--------------
+
+Choose one of the following commands to install Red.
+
+To install without additional config backend support:
+
+.. prompt:: bash
+    :prompts: (redenv) $
+
+    python -m pip install -U pip setuptools wheel
+    python -m pip install -U Red-DiscordBot
+
+Or, to install with PostgreSQL support:
+
+.. prompt:: bash
+    :prompts: (redenv) $
+
+    python -m pip install -U pip setuptools wheel
+    python -m pip install -U "Red-DiscordBot[postgres]"
+
+
+.. note::
+
+    These commands are also used for updating Red
+
+--------------------------
+Setting Up and Running Red
+--------------------------
+
+After installation, set up your instance with the following command:
+
+.. prompt:: bash
+    :prompts: (redenv) $
+
+    redbot-setup
+
+This will set the location where data will be stored, as well as your
+storage backend and the name of the instance (which will be used for
+running the bot).
+
+Once done setting up the instance, run the following command to run Red:
+
+.. prompt:: bash
+    :prompts: (redenv) $
+
+    redbot <your instance name>
+
+It will walk through the initial setup, asking for your token and a prefix.
+You can find out how to obtain a token with
+`this guide <../bot_application_guide>`.
+
+.. tip::
+   If it's the first time you're using Red, you should check our `getting-started` guide
+   that will walk you through all essential information on how to interact with Red.

docs/install_guides/_includes/install-guide-rhel-derivatives.rst

@@ -0,0 +1,26 @@
+.. include:: _includes/linux-preamble.rst
+
+-------------------------------
+Installing the pre-requirements
+-------------------------------
+
+Red Hat Enterprise Linux (RHEL) 8.4-8.x and its derivatives have all required packages available in official repositories.
+Install them with dnf:
+
+.. prompt:: bash
+
+    sudo dnf -y update
+    sudo dnf -y group install development
+    sudo dnf -y install python39 python39-pip python39-devel java-11-openjdk-headless nano git
+
+Set ``java`` executable to point to Java 11:
+
+.. prompt:: bash
+
+    sudo alternatives --set java "java-11-openjdk.$(uname -i)"
+
+.. Include common instructions:
+
+.. include:: _includes/create-env-with-venv.rst
+
+.. include:: _includes/install-and-setup-red-unix.rst

docs/install_guides/_includes/install-python-pyenv.rst

@@ -0,0 +1,34 @@
+----------------------------
+Installing Python with pyenv
+----------------------------
+
+On distributions where Python 3.9 needs to be compiled from source, we recommend the use of pyenv.
+This simplifies the compilation process and has the added bonus of simplifying setting up Red in a
+virtual environment.
+
+.. prompt:: bash
+
+    command -v pyenv && pyenv update || curl https://pyenv.run | bash
+
+**After this command, you may see a warning about 'pyenv' not being in the load path. Follow the
+instructions given to fix that, then close and reopen your shell.**
+
+Then run the following command:
+
+.. prompt:: bash
+
+    CONFIGURE_OPTS=--enable-optimizations pyenv install 3.9.7 -v
+
+This may take a long time to complete, depending on your hardware. For some machines (such as
+Raspberry Pis and micro-tier VPSes), it may take over an hour; in this case, you may wish to remove
+the ``CONFIGURE_OPTS=--enable-optimizations`` part from the front of the command, which will
+drastically reduce the install time. However, be aware that this will make Python run about 10%
+slower.
+
+After that is finished, run:
+
+.. prompt:: bash
+
+    pyenv global 3.9.7
+
+Pyenv is now installed and your system should be configured to run Python 3.9.

docs/install_guides/_includes/install-python38-pyenv.rst

@@ -0,0 +1,34 @@
+----------------------------
+Installing Python with pyenv
+----------------------------
+
+On distributions where Python 3.8 needs to be compiled from source, we recommend the use of pyenv.
+This simplifies the compilation process and has the added bonus of simplifying setting up Red in a
+virtual environment.
+
+.. prompt:: bash
+
+    command -v pyenv && pyenv update || curl https://pyenv.run | bash
+
+**After this command, you may see a warning about 'pyenv' not being in the load path. Follow the
+instructions given to fix that, then close and reopen your shell.**
+
+Then run the following command:
+
+.. prompt:: bash
+
+    CONFIGURE_OPTS=--enable-optimizations pyenv install 3.8.12 -v
+
+This may take a long time to complete, depending on your hardware. For some machines (such as
+Raspberry Pis and micro-tier VPSes), it may take over an hour; in this case, you may wish to remove
+the ``CONFIGURE_OPTS=--enable-optimizations`` part from the front of the command, which will
+drastically reduce the install time. However, be aware that this will make Python run about 10%
+slower.
+
+After that is finished, run:
+
+.. prompt:: bash
+
+    pyenv global 3.8.12
+
+Pyenv is now installed and your system should be configured to run Python 3.8.

docs/install_guides/_includes/linux-preamble.rst

@@ -0,0 +1,5 @@
+.. warning::
+
+    For safety reasons, DO NOT install Red with a root user. If you are unsure how to create
+    a new user on Linux, see `this guide by DigitalOcean
+    <https://www.digitalocean.com/community/tutorials/how-to-create-a-new-sudo-enabled-user-on-ubuntu-20-04-quickstart>`_.