Consider adding support for `Read`

[thomas11]

The Read operation is defined in the Pulumi resource model.

The Read method is responsible for reading the current inputs and state Objects for a resource. Read may be called during a refresh or import of a managed resource or during a preview or update for an external resource.

Allowing users to define a specific command to run on Read could open up new use cases. If you have such a case, please comment below!

This issue is a follow-up from #20.