[Docs] Update linux install docs, redo venv docs (#2920)

* [Docs] Update linux install docs, redo venv docs

Some of our pre-req installation docs needed updating on Windows - this adds new sections for Fedora Linux and Debian/Raspbian Buster, and also removes some unnecessary pre-requirements from other distributions. These have all been tested on fresh VPSes, installing Red both in venvs and with --user, and they all seem to work.

Also, apparently the venv docs were too scary before. These changes try to make it clear that it's easier to use than users may think.

This also includes a little note to stop users from accidentally installing Python with pyenv after installing pre-requirements on Ubuntu.

Signed-off-by: Toby Harradine <tobyharradine@gmail.com>

* Add changelog entries

Signed-off-by: Toby Harradine <tobyharradine@gmail.com>

* Update officially supported platforms in README.md

Signed-off-by: Toby Harradine <tobyharradine@gmail.com>

* Combine sections and add openSUSE

Signed-off-by: Toby Harradine <tobyharradine@gmail.com>

* Include example of using `--user` flag

Signed-off-by: Toby Harradine <tobyharradine@gmail.com>

* Use `py -3.7` on Windows outside of venv

Signed-off-by: Toby Harradine <tobyharradine@gmail.com>

* Reorganise changelog entries

Signed-off-by: Toby Harradine <tobyharradine@gmail.com>

docs/venv_guide.rst

@@ -3,9 +3,23 @@
 =======================================
 Installing Red in a Virtual Environment
 =======================================
+Creating a virtual environment is really easy and usually prevents many common installation
+problems. Firstly, simply choose how you'd like to create your virtual environment:
+
+* :ref:`using-venv` (quick and easy, involves two commands)
+* :ref:`using-pyenv-virtualenv` (recommended if you installed Python with pyenv)
+
+**Why Should I Use a Virtual Environment?**
+
+90% of the installation and setup issues raised in our support channels are resolved when the user
+creates a virtual environment.
+
+**What Are Virtual Environments For?**
+
 Virtual environments allow you to isolate red's library dependencies, cog dependencies and python
-binaries from the rest of your system. It is strongly recommended you use this if you use python
-for more than just Red.
+binaries from the rest of your system. It also makes sure Red and its dependencies are installed to
+a predictable location. It makes uninstalling Red as simple as removing a single folder, without
+worrying about losing your data or other things on your system becoming broken.
 
 .. _using-venv:
 
@@ -17,18 +31,18 @@ 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
-``path/to/venv/`` (or ``path\to\venv\`` on Windows).
+``redenv``.
 
 ~~~~~~~~~~~~~~~~~~~~~~~~
 ``venv`` on Linux or Mac
 ~~~~~~~~~~~~~~~~~~~~~~~~
 Create your virtual environment with the following command::
 
-    python3.7 -m venv path/to/venv/
+    python3.7 -m venv redenv
 
 And activate it with the following command::
 
-    source path/to/venv/bin/activate
+    source redenv/bin/activate
 
 .. important::
 
@@ -42,11 +56,11 @@ Continue reading `below <after-activating-virtual-environment>`.
 ~~~~~~~~~~~~~~~~~~~
 Create your virtual environment with the following command::
 
-    python -m venv path\to\venv\
+    py -3.7 -m venv redenv
 
 And activate it with the following command::
 
-    path\to\venv\Scripts\activate.bat
+    redenv\Scripts\activate.bat
 
 .. important::
 
@@ -86,7 +100,8 @@ Now activate your virtualenv with the following command::
 .. important::
 
     You must activate the virtual environment with the above command every time you open a new
-    shell to run, install or update Red.
+    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.
 
 Continue reading `below <after-activating-virtual-environment>`.