Add our standard PR template (#14)

* Add our standard PR template

* Update main branch name

Author: Maurizio Branca

Diff for: .github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,17 @@
+### Motivation
+<!-- Why this pull request? -->
+
+### Change description
+<!-- What does your code do? -->
+
+### Additional Notes
+<!-- Link any useful metadata: Jira task, GitHub issue, ... -->
+
+### Reviewer checklist
+
+* [ ] PR address a single concern.
+* [ ] PR title and description are properly filled.
+* [ ] Changes will be merged in `main`.
+* [ ] Changes are covered by tests.
+* [ ] Logging is meaningful in case of troubleshooting.
+* [ ] History is clean, commit messages are meaningful (see `CONTRIBUTING.md`) and are well formatted.