Add some docs for using images in a post

Closes #47

docs/usage.md

@@ -11,3 +11,28 @@ on social networks like Twitter and Facebook.
 
 This is the same idea behind the `primary_image` field in the admin.
 
+
+## Images
+
+There are custom `markdown` and `creole` extensions for embedding images that
+have been uploaded via the inline on the post create or edit form in the admin.
+
+You first upload the image or images you want to use in the post by selecting
+them in the file selector in the images section, and then hitting "Save and
+Continue Editing". Once the form reloads, you'll see indicators above each
+uploaded image with a number between two brackets, e.g. `{{ 25 }}`.
+
+This is the syntax if you are using `creale` for adding that image to your
+post. You can just copy and paste that.
+
+If you are using `markdown` however, you will need to use the following
+markup in your post:
+
+    ![Alt Text](25)
+
+or without alt text:
+
+    ![](25)
+
+Adjusting for the number of the image, of course.
+