Add Code Climate badge to README

Hello,

Just wanted to drop you a note to let you know that someone added Fat Free CRM to Code Climate a while back.

I'm the guy who built Code Climate (automated quality metrics for Ruby) and it's completely free for OSS projects as a way to support them.

The code quality reports live here:

https://codeclimate.com/github/fatfreecrm/fat_free_crm

In case you want this information to be available to contributors, this quick PR just adds a dynamic badge to the README (similar to Travis) that displays the code quality GPA.

Let me know if you have any questions, or I can help with anything.

Hope you find Code Climate useful.

Best,

-Bryan