Merge pull request #451 from ydah/add-badge

chore: Add RubyDoc documentation badge to README.md

README.md

@@ -2,6 +2,7 @@
 
 [![Gem Version](https://badge.fury.io/rb/lrama.svg)](https://badge.fury.io/rb/lrama)
 [![build](https://github.com/ruby/lrama/actions/workflows/test.yaml/badge.svg)](https://github.com/ruby/lrama/actions/workflows/test.yaml)
+[![RubyDoc](https://img.shields.io/badge/%F0%9F%93%9ARubyDoc-documentation-informational.svg)](https://www.rubydoc.info/gems/lrama)
 
 Lrama is LALR (1) parser generator written by Ruby. The first goal of this project is providing error tolerant parser for CRuby with minimal changes on CRuby parse.y file.