Add note about permissions in Doc MR template

.gitlab/merge_request_templates/Documentation.md

@@ -15,6 +15,7 @@
 ## Author's checklist
 
 - [ ] Follow the [Documentation Guidelines](https://docs.gitlab.com/ee/development/documentation/) and [Style Guide](https://docs.gitlab.com/ee/development/documentation/styleguide.html).
+- [ ] If applicable, update the [permissions table](https://docs.gitlab.com/ee/user/permissions.html).
 - [ ] Link docs to and from the higher-level index page, plus other related docs where helpful.
 - [ ] Apply the ~Documentation label.