Instruct contributors to use 'ci skip' when submitting doc changes

guides/source/contributing_to_ruby_on_rails.md

@@ -138,6 +138,7 @@ learn about Ruby on Rails, and the API, which serves as a reference.
 You can help improve the Rails guides or the API reference by making them more coherent, consistent, or readable, adding missing information, correcting factual errors, fixing typos, or bringing them up to date with the latest edge Rails.
 
 To do so, make changes to Rails guides source files (located [here](https://github.com/rails/rails/tree/main/guides/source) on GitHub) or RDoc comments in source code. Then open a pull request to apply your changes to the main branch.
+Use `[ci skip]` in your pull request title to avoid running the CI build for documentation changes.
 
 When working with documentation, please take into account the [API Documentation Guidelines](api_documentation_guidelines.html) and the [Ruby on Rails Guides Guidelines](ruby_on_rails_guides_guidelines.html).