CONTRIBUTING.md in grape-0.9.0 vs CONTRIBUTING.md in grape-0.10.0

@@ -30,9 +30,16 @@
 ```
 bundle install
 bundle exec rake
 ```
 
+Run tests against all supported versions of Rails.
+
+```
+appraisal install
+appraisal rake spec
+```
+
 #### Write Tests
 
 Try to write a test that reproduces the problem you're trying to fix or describes a feature that you want to build. Add to [spec/grape](spec/grape).
 
 We definitely appreciate pull requests that highlight or reproduce a problem, even without a fix.