Add Speee fork goals and key changes to README

Document the purpose of this fork (modern Rails support and 0.9.x
backward compatibility) and summarize key changes from upstream
including Rails 7.1-8.1 support, backward compatibility features,
and bug fixes.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: takaokouji

README.md

@@ -9,6 +9,36 @@ of your resources, including their attributes and relationships, to make your se
 JR is designed to work with Rails 5.1+, and provides custom routes, controllers, and serializers. JR's resources may be
 backed by ActiveRecord models or by custom objects.
 
+## Speee Fork
+
+This is the [Speee](https://speee.jp/) fork of [jsonapi-resources](https://github.com/cerebris/jsonapi-resources).
+
+### Goals
+
+- **Modern Rails Support**: Enable compatibility with the latest Rails versions (7.1, 7.2, 8.0, 8.1+)
+- **0.9.x Backward Compatibility**: Maintain compatibility with code written for jsonapi-resources 0.9.x
+
+### Key Changes from Upstream
+
+#### Rails Compatibility
+- Full support for Rails 7.1, 7.2, 8.0, and 8.1
+- Rack 3.0 compatibility fixes
+- Rails 8.2 deprecation warning fixes
+
+#### 0.9.x Backward Compatibility
+- `result.resource` and `result.resources` accessors on operation results
+- `apply_filters` method made public for custom filter implementations
+- PORO (Plain Old Ruby Object) support in `find_fragments`
+
+#### Bug Fixes
+- MySQL compatibility fix for the `quote` method (uses database adapter)
+- Ruby 2.6/2.7 compatibility for `Psych.unsafe_load`
+
+#### Development
+- Docker support for multi-version Rails testing
+- Comprehensive CI matrix covering Ruby 2.6-3.4 and Rails 5.1-8.1
+- SimpleCov integration for test coverage measurement
+
 ## Documentation
 
 Full documentation can be found at [http://jsonapi-resources.com](http://jsonapi-resources.com), including the [v0.10 alpha Guide](http://jsonapi-resources.com/v0.10/guide/) specific to this version.
@@ -24,9 +54,9 @@ which *should* be compatible with JSON:API compliant server implementations such
 
 ## Installation
 
-### Speee Fork
+### Using This Fork
 
-This is the Speee fork of jsonapi-resources. To use this fork, add the following to your application's `Gemfile`:
+To use this fork, add the following to your application's `Gemfile`:
 
 ```ruby
 gem 'jsonapi-resources', github: 'speee/jsonapi-resources', tag: 'v26.1.1'