Adding Lucy's guide

Author: lindaliukas

_posts/2012-04-18-app.markdown

@@ -291,3 +291,5 @@ Test the change by opening the root path in your browser.
 * Guide 4: [Create thumbnail images for the uploads by Miha Filej](/thumbnails)
 * Guide 5: [Add design using HTML & CSS by Alex Liao](/design)
 * Guide 6: [Add Authentication (user accounts) with Devise by Piotr Steininger](/devise/)
+* Guide 7: [Go through additional explanations for the App by Lucy Bain](https://github.com/lbain/railsgirls)
+