Adding a CONTRIBUTING to CoffeeScript.

CONTRIBUTING.md

@@ -0,0 +1,9 @@
+## How to contribute to CoffeeScript
+
+* Before you open a ticket or send a pull request, [search](https://github.com/jashkenas/coffee-script/issues) for previous discussions about the same feature or issue. Add to the earlier ticket if you find one.
+
+* Before sending a pull request for a feature, be sure to have [tests](https://github.com/jashkenas/coffee-script/tree/master/test).
+
+* Use the same coding style as the rest of the [codebase](https://github.com/jashkenas/coffee-script/tree/master/src). If you're just getting started with CoffeeScript, there's a nice [style guide](https://github.com/polarmobile/coffeescript-style-guide).
+
+* In your pull request, do not add documentation to `index.html` or re-build the minified `coffee-script.js` file. We'll do those things before cutting a new release.