How can i copy file to rails public folder when install gem

I wrote a rails plugin, and i wish to make it as a gem. it seems easy
when i use it as a libary code. but it will copy some js, css file to
rails public folder. as a rails plugin, Install.rb will copy file during
the ruby script/plugin install xx process, but how can i achieve this
and convert it as a fully functional rubygem, so i can run 'ruby
gems:install" to deploy it.

any help arreciate.