CONTRIBUTING.md in jekyll_pages_api-0.1.0 vs CONTRIBUTING.md in jekyll_pages_api-0.1.1

@@ -9,9 +9,15 @@
 ```bash
 bundle
 bundle exec rspec
 ```
 
+### Running against Jekyll 3
+
+```bash
+BUNDLE_GEMFILE=gemfiles/jekyll_3.gemfile bundle exec rspec
+```
+
 ## Public domain
 
 This project is in the public domain within the United States, and
 copyright and related rights in the work worldwide are waived through
 the [CC0 1.0 Universal public domain dedication](https://creativecommons.org/publicdomain/zero/1.0/).