Update README.md

plugins/catalog-backend/README.md

@@ -1,16 +1,32 @@
 # Catalog Backend
 
-WORK IN PROGRESS
-
 This is the backend part of the default catalog plugin.
 
-It responds to requests from the frontend part, and fulfills them by delegating
-to your existing catalog related services.
+It comes with a builtin database backed implementation of the catalog, that can store
+and serve your catalog for you.
+
+It can also act as a bridge to your existing catalog solutions, either ingesting their
+data to store in the database, or by effectively proxying calls to an external catalog
+service.
 
 ## Getting Started
 
-After starting the backend, you can issue the `yarn mock-catalog-data` command
-in this directory to populate the catalog with some mock entities.
+This backend plugin can be started in a standalone mode from directly in this package
+with `yarn start`. However, it will have limited functionality and that process is
+most convenient when developing the catalog backend plugin itself.
+
+To evaluate the catalog and have a greater amount of functionality available, instead do
+
+```bash
+# in one terminal window, run this from from the very root of the Backstage project
+cd packages/backend
+yarn start
+
+# open another terminal window, and run the following from the very root of the Backstage project
+yarn lerna run mock-catalog-data
+```
+
+This will launch the full example backend and populate its catalog with some mock entities.
 
 ## Links