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.
Correct percentage value syntax.

Fixes https://www.w3.org/Bugs/Public/show_bug.cgi?id=23297
Merge pull request #14 from silviapfeiffer/readme

Extend README with useful links.
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
Merge pull request #17 from foolip/respec-button

Upgrade ReSpec to commit 1258dea247b803c48e1c52372f9f4a07c487d1c0
Merge pull request #15 from silviapfeiffer/text-select-bug-report

Fix bug-assist box position.
Merge pull request #16 from silviapfeiffer/percentage-value-fix

Correct percentage value syntax.