Update the description for clustered index in TiDB

[cfzjywxk]

Change Request

This repository is ONLY used to solve problems related to DOCS-CN.
For other issues (TiDB, TiKV, etc), please move to other repositories.

Please answer the following questions before submitting your issue. Thanks!

1. Describe what you find is inappropriate or missing in the existing docs.

Since v5.1 the clustered index could be used with tidb-binlog and the previous compatible issues are resolved.

2. Describe your suggestion or addition.

Update the compatibility description for clustered index.

3. Provide some reference materials (documents, websites, etc) if you could.

https://docs.pingcap.com/zh/tidb/stable/clustered-indexes#%E9%99%90%E5%88%B6