Merge pull request #2134 from tianon/contributing

Add devenvironment link to CONTRIBUTING.md

CONTRIBUTING.md

@@ -3,6 +3,10 @@
 Want to hack on Docker? Awesome! Here are instructions to get you started. They are probably not perfect, please let us know if anything feels
 wrong or incomplete.
 
+## Build Environment
+
+For instructions on setting up your development environment, please see our dedicated [dev environment setup docs](http://docs.docker.io/en/latest/contributing/devenvironment/).
+
 ## Contribution guidelines
 
 ### Pull requests are always welcome