Add Code Climate badge to README.md
Add Code Climate badge to README.md

As of this commit, we are getting a clean 4.0 score from Code Climate.
Let's show this off.

Change-Id: I421818691bdc8f721d9f178a775582cc47a28ae4
Reviewed-on: https://gerrit.causes.com/26313
Reviewed-by: Shane da Silva <6f6e68d1df92f30cb4b3ce35260ddf94a402f33d@causes.com>
Tested-by: Joe Lencioni <1dd72cf724deaab5db236f616560fc7067b734e1@causes.com>

brigade/pubsubhub