.github: added pull request template

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,37 @@
+<!-- Kamailio Pull Request Template -->
+
+<!--
+IMPORTANT:
+  - for detailed contributing guidelines, read:
+    https://github.com/kamailio/kamailio/blob/master/.github/CONTRIBUTING.md
+  - pull requests must be done to master branch, unless they are backports
+    of fixes from master branch to a stable branch
+  - backports to stable branches must be done with 'git cherry-pick -x ...'
+  - code is contributed under BSD for core and main components (tm, sl, auth, tls)
+  - code is contributed GPLv2 or a compatible license for the other components
+  - GPL code is contributed with OpenSSL licensing exception
+-->
+
+#### Pre-Submission Checklist
+<!-- Go over all points below, and after creating the PR, tick all the checkboxes that apply -->
+<!-- All points should be verified, otherwise, read the CONTRIBUTING guidelines from above-->
+<!-- If you're unsure about any of these, don't hesitate to ask on sr-dev mailing list -->
+- [ ] Commit message has the format required by CONTRIBUTING guide
+- [ ] Commits are split per component (core, individual modules, libs, utils, ...)
+- [ ] Each component has a single commit (if not, squash them into one commit)
+- [ ] No commits to README files for modules (changes must be done to docbook files
+in `doc/` subfolder, the README file is autogenerated)
+
+#### Type Of Change
+- [ ] Small bug fix (non-breaking change which fixes an issue)
+- [ ] New feature (non-breaking change which adds new functionality)
+- [ ] Breaking change (fix or feature that would change existing functionality)
+
+#### Checklist:
+<!-- Go over all points below, and after creating the PR, tick the checkboxes that apply -->
+- [ ] PR should be backported to stable branches
+- [ ] Tested changes locally
+- [ ] Related to issue #XXXX (replace XXXX with an open issue number)
+
+#### Description
+<!-- Describe your changes in detail -->