minor #2630 Add documentation check to PR template (kbond)

This PR was merged into the 2.x branch.

Discussion
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Add documentation check to PR template

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| Issues        | n/a
| License       | MIT

Hopefully this will prompt contributors to add documentation as required :)

Commits
-------

9d86bbf Add documentation check to PR template

Author: kbond

.github/PULL_REQUEST_TEMPLATE.md

@@ -2,6 +2,7 @@
 | ------------- | ---
 | Bug fix?      | yes/no
 | New feature?  | yes/no <!-- please update src/**/CHANGELOG.md files -->
+| Docs?         | yes/no <!-- required for new features -->
 | Issues        | Fix #... <!-- prefix each issue number with "Fix #", no need to create an issue if none exist, explain below instead -->
 | License       | MIT
 
@@ -13,6 +14,7 @@ Additionally (see https://symfony.com/releases):
  - Always add tests and ensure they pass.
  - For new features, provide some code snippets to help understand usage.
  - Features and deprecations must be submitted against branch main.
+ - Update/add documentation as required (we can help!)
  - Changelog entry should follow https://symfony.com/doc/current/contributing/code/conventions.html#writing-a-changelog-entry
  - Never break backward compatibility (see https://symfony.com/bc).
 -->