fix: update PGID for mariadb service and improve network comments

docker-compose/mariadb/docker-compose.yml

@@ -5,7 +5,7 @@ services:
     container_name: mariadb
     environment:
       - PUID=1000
-      - PGID=1003
+      - PGID=1006
       - MYSQL_ROOT_PASSWORD=ChangeMe123
       - TZ=America/New_York
       - MYSQL_DATABASE=default
@@ -24,7 +24,7 @@ services:
           - mysql  # how to add multiple aliases
           - romm-db
           - db
-networks:    # I don't know why but you have to specify the network 2x. In service, and in this tag area..
+networks:
   homelab:
     name: homelab      # Networks can also be given a custom name
-    external: true      # This option causes compose to join the above network instead of making a _default one, wont work without it though..
+    external: true      # This option causes compose to join the above network instead of making a _default one, also needs to be created first