Quick-fix the top of the install instructions page

[pushfoo]

What's broken?

At the top of this page, we have some oddness as a result of :py:mod and a conflict with something else:
https://api.arcade.academy/en/latest/get_started/install.html#requirements-raspi

This is likely the `pyglet_` link target in the global links include getting lost in the bandaid-rip of 3.0's realease.

Proposed quick fix

Replace this:

arcade/doc/get_started/install.rst

Lines 13 to 15 in 8a41838

	:mod:`pyglet`
	All systems require Python 3.9 or higher on a desktop or laptop device.

With something like this:

Arcade requires a desktop, laptop, or compatible Single-Board Computer (SBC) with:

#. Python 3.9 or higher
#. Graphics drivers with support for either:
    * OpenGL 3.3+
    * GLES 3.1+ with extensions on SBCs

Why a quick fix?

Sphinx extensions and links are prone to compatibility issues. The approach above seems to work, but test it locally via:

1. ./make.py html
2. One of the following:
   • ./make.py server
   • If you have zombie process issues / rebuild loops:
     1. Report it in detail
     2. Use python -m http.server -d build instead
     3. hard refresh pages manually (ctrl-f5 or ctrl-click the refresh icon in the GUI)