### What this PR does / why we need it?
Add kv pool developer guide
### Does this PR introduce _any_ user-facing change?
N/A
### How was this patch tested?
vLLM version: v0.11.0rc3
vLLM main: https://github.com/vllm-project/vllm/commit/v0.11.0
- vLLM version: v0.11.0
- vLLM main:
83f478bb19
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Signed-off-by: Pz1116 <zpbzpb123123@gmail.com>
Signed-off-by: pz1116 <zpbzpb123123@gmail.com>