add gocover badger

Author: patrickdevivo

README.md

@@ -2,6 +2,7 @@
 [![BuildStatus](https://github.com/augmentable-dev/tickgit/workflows/tests/badge.svg)](https://github.com/augmentable-dev/tickgit/actions?workflow=tests)
 [![Go Report Card](https://goreportcard.com/badge/github.com/augmentable-dev/tickgit)](https://goreportcard.com/report/github.com/augmentable-dev/tickgit)
 ![GitHub release (latest SemVer)](https://img.shields.io/github/v/release/augmentable-dev/tickgit)
+[![Coverage](http://gocover.io/_badge/github.com/augmentable-dev/tickgit)](http://gocover.io/github.com/augmentable-dev/tickgit)
 
 ## tickgit 🎟️