Update contributing.md with code style guidelines

contributing.md

@@ -3,6 +3,43 @@
 We're happy to accept contributions in the form of new apps, bug fixes, issues, etc. If you want to help out, add a comment on the issue you want to work on and start hacking. Please open an issue for discussion before submitting framework combinations (eg. Backbone + RequireJS).
 
 
+## Code Style
+
+- Tab indentation
+- Single-quotes
+- Semicolon
+- No trailing whitespace
+- Variables at the top of the scope
+- Multiple variable statements
+- Space after keywords and between arguments and operators
+- Return early
+- JSHint valid
+- Consistency
+
+Example:
+
+```js
+function foo(bar, fum) {
+    var i, l, ret;
+    var hello = 'Hello';
+
+    if (!bar) {
+        return;
+    }
+
+    for (i = 0, l = bar.length; i < l; i++) {
+        if (bar[i] === hello) {
+            ret = fum(out);
+        }
+    }
+
+    return ret;
+}
+```
+
+Read [idiomatic.js](https://github.com/rwldrn/idiomatic.js) for general JavaScript code style best practices.
+
+
 ## Pull Request Guidelines
 
 - Develop in a topic branch (not `master`) and submit against the `labs` folder in the default `gh-pages` branch