[docs][xs]: added notes for React developers.

README.md

@@ -22,3 +22,16 @@ It would:
 * update JS modules in fanstatic
 
 Next, you need to update the template to include correct bundles. In `/templates/datapub/snippets/upload_module.html`, edit the file names of the modules.
+
+Note, if you are developing a React app, e.g., custom `datapub` app, you can use the following attributes passed from the `/templates/datapub/snippets/upload_module.html`:
+
+```html
+<div id="ResourceEditor"
+     data-dataset-id="{{ pkg_name }}"
+     data-api="{{ base_url }}"
+     data-lfs="{{ h.extstorage_lfs_url() }}"
+     data-auth-token="{{ api_key }}"
+     data-organization-id="{{ h.extstorage_organization_name(pkg_name) }}"
+     data-resource-id="{{ resource_id }}">
+</div>
+```