### What this PR does / why we need it?
Revise the KV Pool user guide:
4. Revise parameters for Memcache for better clarity, at notification
that currently heterogeneous protocol setting is not supported (e.g.
enable `device_rdma` and `device_sdma` at the same time, a example
scenario would be data transfer by memcache across different super pods)
5. Modify the condition for Mooncakestore warmup, warmup is now needed
only when `ASCEND_BUFFER_POOL` is enabled.
### Does this PR introduce _any_ user-facing change?
### How was this patch tested?
- vLLM version: v0.17.0
- vLLM main:
8a680463fa
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Signed-off-by: Pz1116 <zpbzpb123123@gmail.com>
Co-authored-by: Chao Lei <leichao139636@163.com>