Add contributing instructions

Author: dalelotts

contributing.md

@@ -0,0 +1,32 @@
+Submitting Issues
+=================
+
+If you are submitting a bug, please create a [jsfiddle](http://jsfiddle.net/) demonstrating the issue.
+
+Contributing code
+=================
+
+To contribute, fork the library and install grunt and dependencies. You need [node](http://nodejs.org/); use [nvm](https://github.com/creationix/nvm) or [nenv](https://github.com/ryuone/nenv) to install it.
+
+```bash
+git clone https://github.com/dalelotts/angular-bootstrap-datetimepicker.git
+cd angular-bootstrap-datetimepicker
+npm install -g grunt-cli
+npm install
+git checkout develop  # all patches against develop branch, please!
+grunt                 # this runs tests and jshint
+```
+
+Very important notes
+====================
+
+ * **Pull pull requests to the `master` branch will be closed.** Please submit all pull requests to the `develop` branch.
+ * **Pull requests will not be merged without unit tests.** 
+ * **Do not include the minified files in your pull request.** 
+
+Grunt tasks
+===========
+
+We use Grunt for managing the build. Here are some useful Grunt tasks:
+
+  * `grunt` The default task lints the code and runs the tests. You should make sure you do this before submitting a PR.