Write doc

Author: sue445

README.md

@@ -152,6 +152,15 @@ open http://localhost:6060/pkg/github.com/ruby-go-gem/go-gem-wrapper/ruby/
 3. Update [_gem/lib/go_gem/version.rb](_gem/lib/go_gem/version.rb)
 4. Run `bundle exec rake release`
 
+### Support new ruby version
+1. Run `go mod vendor`
+2. Run `bundle install`
+3. Add new version to [.github/workflows/matrix.json](.github/workflows/matrix.json)
+4. Update `spec.required_ruby_version` in [_gem/go_gem.gemspec](_gem/go_gem.gemspec)
+5. Add new version to [_tools/ruby_h_to_go/config.yml](_tools/ruby_h_to_go/config.yml)
+6. Run `bundle exec rake ruby_h_to_go` in latest ruby version
+7. Run `bundle exec rake ruby_h_to_go` in [`default_tag`](_tools/ruby_h_to_go/config.yml) ruby version 
+
 ## Original idea
 [Ruby meets Go - RubyKaigi 2015](https://rubykaigi.org/2015/presentations/mmasaki/)