Merge branch 'warn-against-version-managers' into 'master'

Warn Against Version Managers

doc/install/installation.md

@@ -113,6 +113,8 @@ Then select 'Internet Site' and press enter to confirm the hostname.
 
 # 2. Ruby
 
+The use of ruby version managers such as [RVM](http://rvm.io/), [rbenv](https://github.com/sstephenson/rbenv) or [chruby](https://github.com/postmodern/chruby) with GitLab in production frequently leads to hard to diagnose problems. Version managers are not supported and we stronly advise everyone to follow the instructions below to use a system ruby.
+
 Remove the old Ruby 1.8 if present
 
     sudo apt-get remove ruby1.8