README.md: remove outdated file path description (pingcap#2579)

* Update README.md

* Update README.md

* Update README.md

* media, readme: add a contributor image

* readme: update format

Co-authored-by: lilin90 <lilin@pingcap.com>

README.md

@@ -1,35 +1,25 @@
 # TiDB Documentation
 
-This repository stores all the source files of [TiDB Docs at the PingCAP website](https://pingcap.com/docs/stable/), while the [pingcap/docs-cn](https://github.com/pingcap/docs-cn) repository stores all the source files of [TiDB Documentation in Chinese](https://pingcap.com/docs-cn/stable/). If you find documentation issues, feel free to [create an Issue](https://github.com/pingcap/docs/issues/new/choose) to let us know or directly [create a Pull Request](/CONTRIBUTING.md#how-to-contribute) to help fix or update it.
-
-## Docs structure
-
-The general TiDB documentation structure is as follows:
-
-```
-├── TOC.md
-├── how-to
-    ├── get-started
-    ├── deploy
-        ├── orchestrated
-            ├── ansible.md
-            ├── offline-ansible.md
-            ├── docker.md
-    ├── configure
-    ├── maintain
-    ├── troubleshoot
-    ├── ...
-├── reference
-   ├── tools
-    ├── tidb-binlog
-    ├── ...
-├── releases
-├── tidb-in-kubernetes
-├── faq
-├── ...
-...
-```
+Welcome to TiDB documentation!
+
+This repository stores all the source files of [TiDB Docs at the PingCAP website](https://pingcap.com/docs/stable/), while the [pingcap/docs-cn](https://github.com/pingcap/docs-cn) repository stores all the source files of [TiDB Documentation in Chinese](https://pingcap.com/docs-cn/stable/).
+
+If you find documentation issues, feel free to [create an Issue](https://github.com/pingcap/docs/issues/new/choose) to let us know or directly [create a Pull Request](/CONTRIBUTING.md#how-to-contribute) to help fix or update it.
+
+## Documentation versions
+
+Currently, we maintain the following versions of TiDB documentation in different branches:
+
+| Branch name | TiDB docs version |
+| :---------|:----------|
+| [`master`](https://github.com/pingcap/docs/tree/master) | The latest development version |
+| [`release-4.0`](https://github.com/pingcap/docs/tree/release-4.0) | 4.0 RC version |
+| [`release-3.1`](https://github.com/pingcap/docs/tree/release-3.1) | 3.1 stable version |
+| [`release-3.0`](https://github.com/pingcap/docs/tree/release-3.0) | 3.0 stable version |
+| [`release-2.1`](https://github.com/pingcap/docs/tree/release-2.1) | 2.1 stable version |
 
 ## Contributing
 
-See [TiDB Documentation Contributing Guide](/CONTRIBUTING.md) to get started. 🤓
+[<img src="media/contribution-map.png" alt="contribution-map" width="180">](https://github.com/pingcap/community/tree/master/special-interest-groups/sig-docs)
+
+See [TiDB Documentation Contributing Guide](/CONTRIBUTING.md) to become a contributor! 🤓