Describe common development setup for contributors

Author: Macroz

CONTRIBUTING.md

@@ -34,11 +34,19 @@ clojure-mode (version 2.1.1)
 * [Squash related commits together][5].
 * Open a [pull request][4] that relates to *only* one subject with a clear title
 and description in grammatically correct, complete sentences.
-* When applicable, attach ERT unit tests.
+* When applicable, attach ERT unit tests. See below for instructions on running the tests.
+
+## Development setup
+
+1. Fork and clone the repository
+1. Install [Cask][7] as per the instructions there.
+1. With Cask in your path run `cask install` in the repository folder.
+1. Run tests with `make test`.
 
 [1]: https://github.com/clojure-emacs/clojure-mode/issues
 [2]: http://gun.io/blog/how-to-github-fork-branch-and-pull-request
 [3]: http://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html
 [4]: https://help.github.com/articles/using-pull-requests
 [5]: http://gitready.com/advanced/2009/02/10/squashing-commits-with-rebase.html
 [6]: https://github.com/clojure-emacs/clojure-mode/blob/master/CHANGELOG.md
+[7]: https://github.com/cask/cask