Update README.md with supported Redis version

This docs improvement looks pretty helpful and not controversial.

Thanks, useful improvement that can reduce confusion and point people in the right direction, i.e. the docs for their chosen library.

Looks sensible as a diff, but the previous sentence has been removed more than 2 years ago and I don't think this is correct, the adapter doesn't influence the supported version, it's the same commands. All redis versions that are even remotely command and supported should work fine. Closing.