cluster initialization documentation

[amirreza8002]

hi again 👋

https://valkey-py.readthedocs.io/en/latest/clustering.html#creating-clusters it might be worth to add a few lines about creating cluster client connections

the ones i can see

• ValkeyCluster().from_url(...)
• await ValkeyCluster(...).initialize()
• await ValkeyCluster(...) (calls initialize)
• async with ValkeyCluster(...) (calls initialize)

also for sync cluster, it can be used with a context manager with ValkeyCluster()

I'll add these up if it's good with you