*: add 8.2 and 8.3 to README.md (#18700) (#18701)

README.md

@@ -28,6 +28,7 @@ Currently, we maintain the following versions of TiDB documentation in different
 | Branch name | TiDB docs version |
 | :---------|:----------|
 | [`master`](https://github.com/pingcap/docs/tree/master) | The latest development version |
+| [`release-8.2`](https://github.com/pingcap/docs/tree/release-8.2) | 8.2 Development Milestone Release |
 | [`release-8.1`](https://github.com/pingcap/docs/tree/release-8.1) | 8.1 LTS (Long-Term Support) |
 | [`release-8.0`](https://github.com/pingcap/docs/tree/release-8.0) | 8.0 Development Milestone Release |
 | [`release-7.6`](https://github.com/pingcap/docs/tree/release-7.6) | 7.6 Development Milestone Release |