Adds documentation for Ruby Managers.

If Vim isn't well integrated with the Ruby Manager, it will probably use the system Ruby,
sometimes it can be an old version of Ruby causing errors (e.g. hash rocket
vs new syntax), but as the `:TagsGenerate` doesn't show errors to users
(`2>/dev/null`), this commit explains the steps to check if it is well
configured.

README.md

@@ -37,9 +37,26 @@ Vim-Tags requires `ctags` utility. On Ubuntu you can install it with:
 
     sudo apt-get install exuberant-ctags
 
-Please, don't forget to star the repository if you like (and use) the plugin. This will let me know
+On OSX:
+
+    brew install ctags
+
+Please, don't forget to star :star: the repository if you like (and use) the plugin. This will let me know
 how many users it has and then how to proceed with further development :).
 
+Ruby Manager
+-----
+
+If you are using a Ruby Manager such as [chruby](https://github.com/postmodern/chruby), [rvm](http://rvm.beginrescueend.com/), [rbenv](https://github.com/sstephenson/rbenv) etc, be sure to have your Ruby Manager integrated with Vim.
+
+* [Integrating chruby with Vim](https://github.com/postmodern/chruby/wiki/Vim)
+* [Integrating rvm with Vim](http://rvm.io/integration/vim)
+
+A simple way to check this is by executing `bundle show --paths` in your Vim in the command-line mode.
+
+    :!bundle show --paths
+
+If it shows your current Gems (based on your Gemfile) it is probably working fine.
 
 Usage
 -----
@@ -87,7 +104,6 @@ whether the tags generation is required, just like in the custom directories cas
 The plugin will create "Gemfile.lock.tags" file automatically
 
 
-<div id="configuration"></div>
 Configuration
 -------------