chore: add a pull request template (#202)

.github/workflows/pull_request_template.md

@@ -0,0 +1,12 @@
+Closes #number
+
+<!--
+IMPORTANT:
+If your PR doesn't close a particular issue, please, create the issue first and describe the whole context: what you're adding/changing and why you're doing so. And only then open the Pull Request, which would close that issue!
+-->
+
+* [ ] I have updated CHANGELOG.md
+* [ ] I have added unit tests to demonstrate the contribution is correctly implemented
+* [ ] I have run all the tests locally and no test failure was reported
+* [ ] I did not introduce unrelated formatting/whitespace changes in the code base
+* [ ] I did not do unrelated and/or undiscussed refactorings