add integration badge

Author: GrantBirki

README.md

@@ -3,5 +3,6 @@
 [![build](https://github.com/github/hooks/actions/workflows/build.yml/badge.svg)](https://github.com/github/hooks/actions/workflows/build.yml)
 [![test](https://github.com/github/hooks/actions/workflows/test.yml/badge.svg)](https://github.com/github/hooks/actions/workflows/test.yml)
 [![lint](https://github.com/github/hooks/actions/workflows/lint.yml/badge.svg)](https://github.com/github/hooks/actions/workflows/lint.yml)
+[![integration](https://github.com/github/hooks/actions/workflows/integration.yml/badge.svg)](https://github.com/github/hooks/actions/workflows/integration.yml)
 
 A Pluggable Webhook Server Framework written in Ruby