Update readme, reduce length and emphasize our options

- Update for new sourcemaps
- Update for sourcemap adapter
- Add recipe for running two sass tasks at the same time

	I explored adding smart container switching to the plugin but I think it will
	interfere with any type of incremental build / caching that we add. Specifying
	an option isn't a hard request to make to our users either.
Bump version to 1.0.0-alpha