add PR template

Author: Mahmoudz

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,7 @@
+### Thank you for contributing to Laradock.
+
+##### Make sure you completed the basic 3 steps below:
+
+- [] I've read the simple [Contribution Guide](http://laradock.io/contributing).
+- [] I've updated the **documentation**. (refer to [this](http://laradock.io/contributing/#update-the-documentation-site) for how to do so).
+- [] I enjoyed my time contributing and making developer's life easier :)