CONTRIBUTING.md in sinatra-assetpack-0.2.3 vs CONTRIBUTING.md in sinatra-assetpack-0.2.4

@@ -20,8 +20,12 @@
 
 As simple as running `bundle exec rake` command.
 
 The default `rake` task is `rake test`.
 
+If you would like to test multiple ruby version using RVM, try `rvm all do rake test`.
+
+You may setup all ruby version quickly with `rvm all do bundle install`.
+
 ## Syntax
 
 Follow [Ruby Styleguide](https://github.com/styleguide/ruby) by Github and existing code.
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