Redirect /docs to the right page

I've hit this a few times where I want to get to docs so I take whatever
my urlbar gives me and strip out the actual page so I can get to the
root, however that's a 404.

This introduces a super easy way to redirect, which could be handy in
the future as docs get rewritten.

I would much rather do this with a real htaccess file or even just
handle 404s gracefully, but that's not currently an option with GitHub
pages (since we generate our own and don't use a custom domain).
Merge pull request #312 from zpao/docs-redirect

Redirect /docs to the right page