[Doc] Add feature branch policy (#2432)

### What this PR does / why we need it?

This patch add the feature branch policy.

After this patch: maintainers are allowed to create a feature branch.
Feature branches are used for collaboration and must include an RFC
link, merge plan and mentor info.

### Does this PR introduce _any_ user-facing change?

No

### How was this patch tested?

CI passed

- vLLM version: v0.10.0
- vLLM main:
7be5d113d8

Signed-off-by: Yikun Jiang <yikunkero@gmail.com>

README.zh.md

@@ -76,6 +76,7 @@ vllm-ascend有主干分支和开发分支。
 | v0.7.1-dev | Unmaintained | 只允许文档修复 |
 | v0.7.3-dev | Maintained | 基于vLLM v0.7.3版本CI看护, 只允许Bug修复，不会再发布新版本 |
 | v0.9.1-dev | Maintained | 基于vLLM v0.9.1版本CI看护 |
+|rfc/feature-name| Maintained | 为协作创建的[特性分支](https://vllm-ascend.readthedocs.io/en/latest/community/versioning_policy.html#feature-branches) |
 
 请参阅[版本策略](https://vllm-ascend.readthedocs.io/en/latest/community/versioning_policy.html)了解更多详细信息。