Redis#xclaim documentation clarifications

[sriedel]

The documentation for the arguments of Redis#xclaim is confusing and hard to comprehend, and the purpose of the arguments isn't really described.

Cross-referencing with https://redis.io/commands/xclaim#command-options makes the purpose of the arguments a lot clearer.

Especially the first paragraph in the linked documentation can be very important: as a normal user, I probably don't need these. Also, the fact that the :idle and :retrycount parameters are actually used for overwriting the specified attributes of PEL entries and not for filtering can be important, given that with the current reading it's unclear where min_idle_time and :idle differ in function.