Update docs to show required config

[Michael9311]

See #160

[flavorjones]

As mentioned by @dhh here, the maintainers are unable to reproduce what is being described at #160, and this documentation is incorrect.

If you can help us reproduce what's happening, please open an issue so we can fix it! Thank you!

[Z2Flow]

I had the same problem and the solution by @ Eth3rnit3 solved the issue.
Rails 7.1.3.2
Ruby 3.3.0
tailwindcss-rails 2.3.0

I created a simple Rails project:

rails new Play -css tailwind
rails g scaffold Post title:string body:text