Add gem version badge to README

Apparently this is the new thing.

Change-Id: I33a689eb640a1b96ca9a533d12da65dd0585fd38
Reviewed-on: https://gerrit.causes.com/23540
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Joe Lencioni <joe.lencioni@causes.com>
Add code climate badge to README

This adds a badge that shows a heuristic "code climate" score.
`scss-lint` currently has a score of 3.98 (but rounds up to a perfect
4.0 in the badge), so including this allows us to show off the quality
of our code.

Change-Id: Ic2bab3a3410221a965faa961f4d0361fb6f05861
Reviewed-on: https://gerrit.causes.com/23541
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Joe Lencioni <joe.lencioni@causes.com>