Add reminder about using correct app

Author: SteveBarnett

sites/en/intro-to-rails/getting_started.step

@@ -55,7 +55,11 @@ steps do
   step do
     message <<-MARKDOWN
 Open the suggestotron folder as a project in your text editor.
+  MARKDOWN
+
+  tip "Close any files that are already open. They might be from yesterday's `test_app`, and we want to make sure that we're editing files in today's `suggestotron` app."
 
+  message <<-MARKDOWN
 In **Sublime Text 2**, you can use the `Project > Add Folder to Project...` menu option:
 
 ![Sublime Text Project menu screenshot](img/sublime_add_folder_to_project.png)