Add pull request template for Pyodide Github repository [skip ci] (#1925)

Co-authored-by: Hood Chatham <roberthoodchatham@gmail.com>

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,23 @@
+<!-- Thank you for contributing to Pyodide! All improvements are welcome,
+     so don't be afraid to make a PR. -->
+
+<!-- [IMPORTANT] Note on CI failures: 
+     Currently, we are having issues with selenium-based tests.
+     Don't panic if the CI fails on your PR because of timeouts.
+     It's probably not your fault. We will investigate :) -->
+
+### Description
+
+<!-- Please explain what your PR is about:
+     - reasoning for the change
+     - some details of updated code
+     - any noteworthy choices to be aware of
+	Please refer to any related issues by #<issue_id> -->
+
+### Checklists
+
+Not all of these steps are necessary for every PR.
+
+- [ ] Add a [CHANGELOG](https://github.com/pyodide/pyodide/blob/main/docs/project/changelog.md) entry or explain why an entry is not needed
+- [ ] Add / update tests
+- [ ] Add new / update outdated documentation