*: Dumpling merged into TiDB

[okJiang]

What problem does this PR solve?

Update the README.md to tell others the information that Dumpling merged into TiDB.

What is changed and how it works?

• update the README.md

Check List

Tests

• No code

Release note

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• lichunzhu

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[lichunzhu]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 407d010