Add pull request template

Author: hovaesco

.github/pull_request_template.md

@@ -0,0 +1,21 @@
+<!-- Thank you for submitting a pull request! Find more information in our development guide at https://github.com/trinodb/trino/blob/master/.github/DEVELOPMENT.md and contact us on #python-client in Slack. -->
+<!-- Provide an overview of the PR for maintainers and reviewers. -->
+## Description
+
+
+
+<!-- Provide a user-friendly explanation, keep it brief if it isn't user-visible. -->
+## Non-technical explanation
+
+
+
+<!-- Mark the appropriate option with an (x). Propose a release note if you can. -->
+## Release notes
+
+( ) This is not user-visible and no release notes are required.
+( ) Release notes are required, please propose a release note for me.
+( ) Release notes are required, with the following suggested text:
+
+```markdown
+* Fix some things. ({issue}`issuenumber`)
+```