Add pull request template

Author: nifadyev

.github/pull_request_template.md

@@ -0,0 +1,11 @@
+## #(issue number): Summarize your changes
+
+<!--Please include the reasons behind these changes and any relevant context.
+This project only accepts pull requests related to open issues -->
+<!--- Special phrase to auto-close the issue that your PR fixes -->
+Closes # (issue number)
+
+## Checklist before requesting a review
+
+- [ ] Have you followed the guidelines in [CONTRIBUTING.md](../CONTRIBUTING.md)?
+- [ ] Have you performed a self-review?