Add a github pull request template

Reviewed-by: Richard Levitte <levitte@openssl.org>

GH: #1770

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,17 @@
+<!--
+Thank you for your pull request. Please review below requirements.
+
+Contributors guide: https://github.com/openssl/openssl/blob/master/CONTRIBUTING
+-->
+
+##### Checklist
+<!-- Remove items that do not apply. For completed items, change [ ] to [x]. -->
+- [ ] documentation is added or updated
+- [ ] tests are added or updated
+- [ ] CLA is signed
+
+##### Description of change
+<!-- Provide a description of the changes.
+
+If it fixes a github issue, add Fixes #XXXX.
+-->