doc: updated README.md to remove broken link

- Removed the broken link in README.md file about `backward compatibility`.
- The section 
`# About update and backward compatibility` was removed in an earlier PR (https://github.com/docker/compose/pull/10889/files).

Signed-off-by: Lokesh Kumar <[email protected]>

README.md

@@ -1,6 +1,5 @@
 # Table of Contents
 - [Docker Compose v2](#docker-compose-v2)
-- [About update and backward compatibility](#about-update-and-backward-compatibility)
 - [Where to get Docker Compose](#where-to-get-docker-compose)
     + [Windows and macOS](#windows-and-macos)
     + [Linux](#linux)
@@ -84,4 +83,4 @@ If you find an issue, please report it on the
 Legacy
 -------------
 
-The Python version of Compose is available under the `v1` [branch](https://github.com/docker/compose/tree/v1).
+The Python version of Compose is available under the `v1` [branch](https://github.com/docker/compose/tree/v1).