Turn off confusing view source link

[pushfoo]

TL;DR: Turn off .rst source link mentioned in #2859

What's fixed?

	Live	This PR
Page view
Problem?		None

How's it fixed?

html_show_sourcelink = False in conf.py.

This is the simplest, most durable approach::

1. Turning it off is the simplest fix
   • pyglet does this
   • NumPy does it with extra steps via a link to their GitHub repo README.md
2. Hide it at the bottom of the page in tiny gray font (PyMunk)

What I've tested on Chrome:

• Building doc locally
• Viewing it in desktop, tablet, and mobile preview modes
• Click-to-copy on code examples still works