How to Upgrade Rails to 4.2?

问题

I Want to upgrade my Rails application properly from 3.2.12 to 4.2 ...

someone send me this link: http://edgeguides.rubyonrails.org/upgrading_ruby_on_rails.html

at the moment I'm trying to upgrade from 3.2.12 to 4.0 ... i'm hanging on step 5.4:

Rails 4.0 no longer supports loading plugins from vendor/plugins. 
You must replace any plugins by extracting them to gems and adding them to your Gemfile. 
If you choose not to make them gems, you can move them into, say, lib/my_plugin/* 
and add an appropriate initializer in config/initializers/my_plugin.rb.

Okay thats no Problem to copy from vendor/plugins to lib ... but how do I have to set up the initializers? ...