Add PR checkbox for theme documentation (Shopify#1516)

* Add PR checkbox for theme documentation

* Update .github/PULL_REQUEST_TEMPLATE.md

.github/PULL_REQUEST_TEMPLATE.md

@@ -22,6 +22,7 @@ _Please include a link to a demo store that includes preconfigured sections and
 
 **Checklist**
 - [ ] Added PR summary for [release notes](https://themes.shopify.com/themes/dawn/styles/default#ReleaseNotes)
+- [ ] Notified the [help.shopify.com](https://help.shopify.com) team about updates to theme settings (current contact: Kimli)
 - [ ] Followed [theme code principles](https://github.com/Shopify/dawn/blob/main/.github/CONTRIBUTING.md#theme-code-principles)
 - [ ] Linted with [Theme Check](https://github.com/Shopify/theme-check)
 - [ ] Tested on [mobile](https://shopify.dev/themes/store/requirements#mobile-browser-requirements)