Should have branches against different version of Rails

[JuanitoFatas]

When all translation is done. Follow the same practice as rails/rails do. Then we could have 4-2-stable, 5-0-stable, et cetera, translations available.

http://docrails-tw.github.io/ always have the edge one.

http://docrails-tw.github.io/rails5 could be the translation of Rails 5.

[JuanitoFatas]

When every post has been translated (except for release notes), then consider this issue.