fixed needed rails version

README.md

@@ -25,7 +25,7 @@ Getting Started
 
 ```
      zammad@shell> cd zammad
-     zammad@shell> gem install rails
+     zammad@shell> gem install rails --version '~> 3.2.0'
      zammad@shell> vi Gemfile # enable libv8, execjs and therubyracer if needed!
      zammad@shell> sudo bundle install
 ```