Add Github Pull Request Template

.github/pull_request_template.md

@@ -0,0 +1,7 @@
+Thank you for your contribution!
+
+Before creating a Pull Request, please make sure to
+* read https://github.com/igniterealtime/Smack/wiki/Guidelines-for-Smack-Developers-and-Contributors
+* run `gradle check` successfully in order to make sure that your code does not break any JUnit tests and is conform to the projects code style.
+* (if applicable) mention any Jira issue codes (eg. `SMACK-XXX`) in the *body* of your commit message (not the header), so that Jira automatically links the PR to the issue.
+* squash your commits if possible/sensible.