README.md in prime-0.1.2 vs README.md in prime-0.1.3

- old
+ new

@@ -1,6 +1,8 @@
 # Prime
 
+[![CI](https://github.com/ruby/prime/actions/workflows/test.yml/badge.svg)](https://github.com/ruby/prime/actions/workflows/test.yml)
+
 Prime numbers and factorization library.
 
 ## Installation
 
 Add this line to your application's Gemfile: