Flesh out the README

README.md

@@ -2,7 +2,12 @@
 
 ## Introduction
 
-A module to facilitate image discovery for Islandora repository items.
+A module to facilitate image discovery for Islandora repository items. Image discovery looks for images in the following places and will use (and cache) the first one found:
+
+* contents of a Media field, `field_representative_image` on the node
+* an "Islandora thumbnail", i.e., a media that is "Media of" the node (using `field_media_of`) with a Media Use (`field_media_use`) taxonomy term with External URI (`field_external_uri`) equal to "http://pcdm.org/use#ThumbnailImage"
+* a first child's Islandora thumbnail media, i.e. the Islandora thumbnail of the node with lowest weight (`field_weight`) that is a Member Of (`field_member_of`) the node in question. If not found on the first direct child, it will look at the first child's first child, and so forth to a depth of 3. 
+
 
 ## Requirements
 
@@ -18,14 +23,34 @@ further information.
 
 ## Usage
 
-This module allow for image discovery on parent aggregate objects such as
+This module allows for image discovery on parent aggregate objects such as
 collections, compounds and paged objects.
 
 ## Configuration
 
+### Adding a "Representative Image" field to your content type
+
+To override the use of the "Islandora" thumbnail, you can add a new field to each of your applicable content types. To do this:
+
+1. In the "Manage fields" page for your content type, choose "Create a new field".
+1. In the "Add a new field" list, choose "Media" (if on Drupal < 10.2, this is "Reference > Media")
+1. Set the new field's label to "Representative image" so that the machine name of this field is `field_representative_image`. This machine name must be set; you can change the label later if you wish. 
+1. On the next page, in the "Type of item to reference" setting, choose "Media" and leave the "Allowed number of values" at 1.
+1. On the next page, in the "Media type" checkboxes, choose "Image".
+1. Click on "Save settings".
+
+If you are adding the field to more than one content type, you should choose "Re-use an existing field" on subsequent content types.
+
+### Using the image in Views
+
 When configuring a content view, add and configure the virtual field
 "DGI Image Discovery Discovered Image".
 
+### Using the image in Content Display
+
+Under "Manage display" for a content type, you can enable the pseudo-field
+"DGI Image Discovery Discovered Image".
+
 ## Troubleshooting/Issues
 
 Having problems or solved a problem? Contact