Adds TeamCity CodeBetter build badge

This PR adds TeamCity CodeBetter build badge. For those who aren't familiar:
 > TeamCity is the primary build server for the Microsoft development platform including .NET. CodeBetter [hosts TeamCity](http://teamcity.codebetter.com/) for the majority of OSS projects in the Microsoft development platform including .NET.

I've followed the conventions used by the other badges/shields and used npm's as a base for this one.

If there is anything you need changed or added let me know.