Update contribution guidelines

CONTRIBUTING.md

@@ -1,9 +1,17 @@
-We are always looking for the quality contributions and will be happy to accept your Pull Requests as long as those adhere to some basic rules:
+This project would not be possible without your help and support and we appreciate your willingness to contribute!
 
-* Please make sure that your contribution fits well in the project's context:
-  * we are aiming at rebuilding Foundation directives in pure AngularJS, without any dependencies on any external JavaScript library;
-  * the only dependency should be Foundation CSS and its markup structure;
+## Issues
+
+When reporting an issue, please create a demonstration of your issue using [plunker](http://plnkr.co/) or a similar service. We prefer to reserve issue reporting for actual issues. Instead of simply asking for a new feature, why not create it yourself and open a pull request? :wink:
+
+## Pull Requests
+
+Please make sure that your contribution fits according to the project's goals:
+
+  * we are aiming at rebuilding Foundation directives in pure AngularJS, without any dependencies on any external JavaScript library
+  * the only dependency should be Foundation CSS and its markup structure
+  * behavior should be properly tested
   * directives should be html-agnostic as much as possible which in practice means:
-        * templates should be referred to using the `templateUrl` property
-        * it should be easy to change a default template to a custom one
-        * directives shouldn't manipulate DOM structure directly (when possible)
+    * templates should be referred to using the `templateUrl` property
+    * it should be easy to change a default template to a custom one
+    * directives shouldn't manipulate DOM structure directly (when possible)