Add ember-data dependency to the quickstart

Author: barryofguilder

tests/dummy/app/templates/docs/quickstart.md

@@ -2,10 +2,16 @@
 
 ## 1. Install AddonDocs
 
-```
+```sh
 ember install ember-cli-addon-docs
 ```
 
+[Ember Data](https://github.com/emberjs/data) is a required peer dependency, so if you're not already using it in your addon, you'll need to install it.
+
+```sh
+ember install ember-data
+```
+
 ## 2. Install ember-cli-addon-docs-yuidoc
 
 API docs are autogenerated from comments in your source code, and require an additional plugin to be installed.