`tansu cat consume --partition-max-bytes` description seems wrong

As mentioned in #279, the description for the `tansu cat consume --partition-max-bytes` is currently "The partition to consume from", which doesn't seem to make any sense compared to the argument name and the fact that it takes an integer as input.

I looked through the source code and couldn't really work out what the flag is expected to do (I'm a Rust rookie).