[Piglit] Piglit website in sphinx

[Jordan Justen]

Although I doubt it generates much traffic, I wanted to try to convert
the https://piglit.freedesktop.org/ homepage into an 'auto-building'
gitlab branch.

I think the current site was built by ikiwiki, but I was after
spending way more time that I hoped, I still was unable to reproduce
the site without lots of extra undesirable links.

So, I tried converting it to sphinx. Of course, I expected it would
look somewhat different with sphinx. This change proved much easier,
and I think looks pretty good:

https://jljusten.pages.freedesktop.org/piglit/

The source code is here in this branch:

https://gitlab.freedesktop.org/jljusten/piglit/commits/website

It is setup such that we could add a small 'website' branch to the
piglit repo. The branch's history would be detacted from the source
code history.

Then, if we need to change the piglit website again, in, say a decade
or so :), it'll be a bit simpler.

Does it look ok, and does it seem like an ok plan?

-Jordan