add badge on readme

Author: fedetaglia

README.md

@@ -1,5 +1,7 @@
 # BMT Ruby
 
+![build BMT](https://github.com/bugcrowd/bmt-ruby/actions/workflows/build.yml/badge.svg?branch=main)
+
 While the Content and Structure is defined in the [Methodology Taxonomy](https://github.com/bugcrowd/methodology-taxonomy), this defines methods to allow for easy handling of methodologies logic.  This gem is used and maintained by [Bugcrowd Engineering](https://bugcrowd.com).
 
 ## Installation