Slightly more descriptive readme
More keyboard focus indication

Further doubling up of :hover styles to also happen on :focus. Note the
patch for missing styles in Mozilla's official sandstone_guide.css (if
that could be pushed upstream to Moz's style guide itself, that'd be
sweet).
Make download/github tooltips trigger on keyboard

A problem with tipsy's approach perhaps, as it assumes that it should be
EITHER mouseenter/mouseleave OR focus/blur. Dirty solution while I
devise a fix to propose upstream to tipsy's repo is to run tipsy twice,
which should not - from quick testing - have any negative impact.
Merge pull request #9 from patrickhlauke/gh-pages

More descriptive readme and further keyboard focus indication fixed