Update README.md

Author: nagstler

README.md

@@ -3,6 +3,7 @@
 # RubyMCP
 
 [![Build](https://github.com/nagstler/ruby_mcp/actions/workflows/build.yml/badge.svg)](https://github.com/nagstler/ruby_mcp/actions/workflows/build.yml)
+[![RuboCop](https://github.com/nagstler/ruby_mcp/actions/workflows/rubocop.yml/badge.svg)](https://github.com/nagstler/ruby_mcp/actions/workflows/rubocop.yml)
 [![Test](https://github.com/nagstler/ruby_mcp/actions/workflows/test.yml/badge.svg)](https://github.com/nagstler/ruby_mcp/actions/workflows/test.yml)
 [![codecov](https://codecov.io/github/nagstler/ruby_mcp/graph/badge.svg?token=SG4EJEIHW3)](https://codecov.io/github/nagstler/ruby_mcp)