Add note to follow PR template, add checklist for AI acknowledgment (#19289)

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,3 +1,7 @@
+<!--
+⚠️ Pull requests that do not follow the template may be closed without review.
+-->
+
 ## Description
 
 <!-- Please provide a brief summary of your changes -->
@@ -11,3 +15,5 @@
 - [ ] (If changing the API or CLI) I’ve documented the changes I’ve made (in the `docs/` directory).
 - [ ] (If the change is user-facing) I’ve added my changes to `changelog_unreleased/*/XXXX.md` file following `changelog_unreleased/TEMPLATE.md`.
 - [ ] I’ve read the [contributing guidelines](https://github.com/prettier/prettier/blob/main/CONTRIBUTING.md).
+- [ ] I did _not_ use AI to generate this PR.
+- [ ] (If the above is not checked) I have reviewed the AI-generated content before submitting.

CONTRIBUTING.md

@@ -92,6 +92,8 @@ Prettier is an opinionated formatter and is not accepting pull requests that add
 
 The project uses ESLint for linting and Prettier for formatting. If your editor isn't set up to work with them, you can lint and format all files from the command line using `yarn fix`.
 
+Please follow the [PR template](.github/PULL_REQUEST_TEMPLATE.md) when opening pull requests, pull requests that do not follow the template may be closed without review.
+
 After opening a PR, describe your changes in a file in the `changelog_unreleased` directory following the template [`changelog_unreleased/TEMPLATE.md`](changelog_unreleased/TEMPLATE.md) and commit this file to your PR. You can use `yarn generate-changelog` to generate a changelog file. Please see comments of the script file for usage.
 
 ## Other