Extend README with useful links.

Extend README a bit so people don't have to go chasing for the right
links.
Fix bug-assist box position.

In commit https://dvcs.w3.org/hg/text-tracks/rev/1c6d33305c80 the
styling of the bug-assist box seems to have been removed by the
bug-assist.js script. This patch re-introduces the most important
styles.
Upgrade ReSpec to commit 1258dea247b803c48e1c52372f9f4a07c487d1c0

This ReSpec commit got rid of the button in the static version of the
spec. Unfortunately, the commit immediately following it broke the
respec2html.js script, so we cannot upgrde and further until that is
fixed: https://github.com/darobin/respec/pull/294
Add missing </li>