Rename redis to valkey in readme

Certainly the code samples should all say valkey. Other things I'm not so sure about. I'll need to go over the Valkey website docs and command references and whatnot to update URLs.

Lots of open questions before this can land:
- Does Valkey use the `redis://` protocol identifier? Is there a `valkey://`?
- Are all the config properties renamed from redis* to valkey*?

Also, how was this repo forked? Was it from a historical commit before a license change? I suppose Redis inc took over the `redis` module but `ioredis` wasn't affected, however as Redis introduced proprietary features I'm guessing `ioredis` added support and we wanted to revert it?

Signed-off-by: Thomas Hunter II <[email protected]>