doc: update CHANGELOG.md and CONTRIBUTING.md

[skip ci]

Author: flavorjones

CHANGELOG.md

@@ -1,6 +1,7 @@
 ## next / unreleased
 
 * Update to [Tailwind CSS v3.4.1](https://github.com/tailwindlabs/tailwindcss/releases/tag/v3.4.1) from v3.4.0 by @flavorjones
+* Fix `password` form field styling in generated scaffold forms. (#304, #307) @flavorjones
 
 
 ## v2.2.0 / 2023-01-04

CONTRIBUTING.md

@@ -2,6 +2,27 @@
 
 This doc is a brief introduction on modifying and maintaining this gem.
 
+
+## Testing this gem
+
+### Running the test suite
+
+The unit tests are run with `bundle exec rake test`
+
+There is an additional integration test which runs in CI, `test/integration/user_journey_test.sh` which you may also want to run.
+
+
+### Testing in a Rails app
+
+If you want to test modifications to this gem, you must run `rake download` once to download the upstream `tailwindcss` executables.
+
+Then you can point your Rails application's `Gemfile` at the local version of the gem as you normally would:
+
+``` ruby
+gem "tailwindcss-rails", path: "/path/to/tailwindcss-rails"
+```
+
+
 ## Updating to the latest upstream tailwindcss version
 
 Update `lib/tailwindcss/upstream.rb` with the upstream version.