The Rails Guides are static HTML, so it's incredibly easy to generate and preview them locally.
To get started:
git clone [email protected]:rails/rails.git
cd rails
bundle install --without db
cd guides
bundle exec rake guides:generate:html
open output/index.html
The docs themselves are written in plain old Markdown, in the guides/source
directory.
Just edit them and run bundle exec rake guides:generate:html
again to update your HTML.
Make sure to follow the Guides Guidelines.
When you're ready to make a pull request, fork rails/rails on GitHub, add your fork as a remote, push to it, and fire off your request.