Add pull request template

Author: StevenRenaux

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,13 @@
+| Q                        | A        |
+|--------------------------|----------|
+| Gotenberg version?       | 8.x      |
+| Bug fix?                 | yes/no   |
+| New feature?             | yes/no   |
+| Backward Compatibility ? | yes/no   |
+| Issues                   | Fix #... |
+
+## Description
+
+<!-- 
+    Explain the feature/bugfix and explain why you chose this implementation.
+-->