docs: point Development section to develop.sh (fix stale ln -s for V2)

[pengfaming]

What

The Development section of the README instructs users to run:

python setup.py build
ln -s build/lib.linux-x86_64-cpython-38/deep_ep_cpp.cpython-38-x86_64-linux-gnu.so

This command is stale. Since the V2 refactor the extension is named deep_ep._C (see setup.py), so build/lib.linux-x86_64-cpython-38/deep_ep_cpp...so no longer exists and the ln -s step fails / links nothing usable.

The repo already ships a correct development script, ./develop.sh, which builds the extension and creates the proper symbolic links for the SO files.

Why

Users following the README's development instructions hit a broken command. Pointing to ./develop.sh gives them the maintained, working path.

How I checked

• Confirmed the extension is built as deep_ep._C in setup.py (V2 naming).
• Confirmed develop.sh exists in the repo root and does the build + symlink step.
• Verified tests/elastic/test_ep.py etc. are still referenced after the change.

[ds-review-bot]

⚠️ 审查 agent 未正常完成，未产生评论。Agent 可能已脱轨。请重新触发审查。

🤖 ds-review-bot Code Review

v6

⚠️ 未完成评审（upstream_error：模型上游服务不可用）

v5

文档修复：README 的 Development 部分不再使用过时的 python setup.py build + ln -s build/lib.../deep_ep_cpp...so 命令，改为指向仓库内维护的 ./develop.sh 脚本。经核实：setup.py 中扩展模块自 V2 起命名为 deep_ep._C，旧的 deep_ep_cpp SO 文件已不存在；develop.sh 存在于仓库根目录，负责清理旧构建产物、执行构建并在 deep_ep/ 下创建正确的 SO 符号链接；测试命令（tests/elastic/test_ep.py、test_pp.py 等）仍被正确引用。变更仅涉及文档，内容准确，符合预期。

v4p

本 MR 更新 README 的 Development 部分，将过时的 python setup.py build + ln -s build/lib.../deep_ep_cpp...so 命令替换为仓库已有的 bash ./develop.sh。经核对 setup.py 中扩展名已改为 deep_ep._C，且 develop.sh 会自动查找 build 产物并在 deep_ep/ 下创建正确符号链接，变更准确解决了文档失效问题。整体评估：改动简洁、与现有脚本一致，未发现需要修改的问题。

Files reviewed: 1

Issues found: ❌ Review incomplete — LLM response could not be parsed
Error: [v6] upstream_error：模型上游服务不可用