Fix installation on guides/source/action_text_overview.md

gem 'image_proccessing' is required.

guides/source/action_text_overview.md

@@ -46,6 +46,8 @@ happens after every keystroke, and avoids the need to use execCommand at all.
 ## Installation
 
 Run `rails action_text:install` to add the Yarn package and copy over the necessary migration.
+Also, you need to set up Active Storage for embedded images and other attachments.
+Please refer to the [Active Storage Overview](active_storage_overview.html) guide.
 
 ## Examples