add contribution guidelines from dev

CONTRIBUTING.md

@@ -0,0 +1,20 @@
+## Contributing
+
+Please keep the [issue tracker](http://github.com/hakimel/reveal.js/issues) limited to **bug reports**, **feature requests** and **pull requests**.
+
+
+### Personal Support
+If you have personal support or setup questions the best place to ask those are  [StackOverflow](http://stackoverflow.com/questions/tagged/reveal.js).
+
+
+### Bug Reports
+When reporting a bug make sure to include information about which browser and operating system you are on as well as the necessary steps to reproduce the issue. If possible please include a link to a sample presentation where the bug can be tested.
+
+
+### Pull Requests
+- Should follow the coding style of the file you work in, most importantly:
+  - Tabs to indent
+  - Single-quoted strings
+- Should be made towards the **dev branch**
+- Should be submitted from a feature/topic branch (not your master)
+- Should not include the minified **reveal.min.js** or **reveal.min.css** files