[Docker] Update README with Docker support

README.md

@@ -24,6 +24,7 @@
   * All things are vimized: irb, postgres command line, etc.
 
 *Linux/Ubuntu is not supported! If it works, great. If it doesn't, please don't complain. You may need to install zsh if you don't already have it.*
+*That being said, check the Docker section below*
 
 ## Mailing List
 
@@ -281,6 +282,20 @@ of plugins above to learn more.
 * [Overriding vim settings with ~/.vimrc.after and friends](doc/vim/override.md)
 * [Adding your own vim plugins](doc/vim/manage_plugins.md)
 
+## Testing with Docker
+
+We can use Docker to test some changes in a **Linux** Container.
+
+Assuming your host system has Docker & Docker Compose properly installed, run:
+
+    docker-compose run dotfiles
+
+This will build the container image it never built it before (which may take a while -- future times will be faster) and then run a `zsh` session inside that container for you.
+There you can play around, test commands, aliases, etc.
+
+*Warning*: this repo is primarly OSX oriented. So any support for Linux can only be done with the help of the community.
+
+
 ## Misc
 
 * [Credits & Thanks](doc/credits.md)
@@ -316,11 +331,9 @@ brew uninstall vim
 rvm system do brew install vim --with-lua
 ```
 
-
 ### [Pry](http://pry.github.com/)
 
 Pry offers a much better out of the box IRB experience with colors, tab completion, and lots of other tricks. You can also use it
 as an actual debugger by installing [pry-nav](https://github.com/nixme/pry-nav).
 
 [Learn more about YADR's pry customizations and how to install](doc/pry.md)
-