chore: Docs bullet point in PR checklist (#2718)

.github/pull_request_template.md

@@ -6,3 +6,4 @@
 - [ ] Additional tests are included, if changing behaviors/core code that is testable.
 - [ ] Proper Copyright + License headers added to applicable files (Generally, we stick to "The ZMK Contributors" for copyrights to help avoid churn when files get edited)
 - [ ] [Pre-commit](https://zmk.dev/docs/development/local-toolchain/pre-commit) used to check formatting of files, commit messages, etc.
+- [ ] Includes any necessary [documentation changes](https://zmk.dev/docs/development/contributing/documentation).