-#### VOCABULARY_URL
-Local path, or any URL that allows cross-origin requests. See
-[Vocabulary JSON file example](public/vocabulary-example.json).
+### API_HOST
+
+The Arvados base URL.
+
+The `REACT_APP_ARVADOS_API_HOST` environment variable can be used to set the default URL if the run time configuration is unreachable.
+
+## FILE_VIEWERS_CONFIG_URL
+Local path, or any URL that allows cross-origin requests. See:
+
+[File viewers config file example](public/file-viewers-example.json)
+
+[File viewers config scheme](src/models/file-viewers-config.ts)
+
+To use the URL defined in the Arvados cluster configuration, remove the entire `FILE_VIEWERS_CONFIG_URL` entry from the runtime configuration. Found in `/config.json` by default.
+
+## Plugin support
+
+Workbench supports plugins to add new functionality to the user
+interface. For information about installing plugins, the provided
+example plugins, see [src/plugins/README.md](src/plugins/README.md).
+