expand docs: def bucket({_file, scope}), do: scope.bucket || bucket()

[niccolox]

I am using Waffle, Waffle Ecto, Phoenix, and an S3 image store.

Works great, thanks for bringing life again to this ecosystem.

I see in a recent PR it's now possible to define buckets based on scope, this is a great new feature, been wanting it for ages.

def bucket({_file, scope}), do: scope.bucket || bucket()

Can I get some clues via a recipe or doc or example?

How do I need to use the Store with Scope in the context of Ecto and Phoenix?

I suspect bucket scope might effect

1. Definition ImageUploader: what examples of definitions for a bucket?
2. How do I get scope into the ImageUploader? I want the scope to be passed in via the normal Phoenix form, what mods allow me to use the scope in that form?
3. Do I need to make a custom changeset or function?
4. Schema i.e. Post, do I need a changeset for Store of the scope?