Add more setup instructions

Author: angrybrad

README.md

@@ -31,6 +31,10 @@ composer require craftcms/google-cloud
 
 ## Setup
 
+Your Google Cloud bucket must use Google's `Fine grained` (per object) permissions, not `Uniform` (per bucket).
+
+On the permissions table for the new bucket, grant `Storage Object Viewer` to `allUsers`. The `Storage Admin` role should be granted to the service account the credentials are tied to.
+
 To create a new asset volume for your Google Cloud Storage bucket, go to Settings → Assets, create a new volume, and set the Volume Type setting to “Google Cloud Storage”.
 
 > **Tip:** The Project ID, Bucket, and Subfolder settings can be set to environment variables. See [Environmental Configuration](https://docs.craftcms.com/v3/config/environments.html) in the Craft docs to learn more about that.