Contribution.md: add contribution map icon and link (tikv#7041)

CONTRIBUTING.md

@@ -2,8 +2,9 @@
 
 Thanks for your interest in contributing to TiKV! This document outlines some of the conventions on building, running, and testing TiKV, the development workflow, commit message formatting, contact points and other resources.
 
-If you need any help or mentoring getting started, understanding the codebase, or making a PR (or anything else really), please ask on [Slack](https://join.slack.com/t/tikv-wg/shared_invite/enQtNTUyODE4ODU2MzI0LTgzZDQ3NzZlNDkzMGIyYjU1MTA0NzIwMjFjODFiZjA0YjFmYmQyOTZiNzNkNzg1N2U1MDdlZTIxNTU5NWNhNjk), or [WeChat](./README.md#WeChat).
+TiKV has many dependent repositories. If you don't know where to start, please click on the contributor icon below to get you on the right contributing path.
 
+[<img src="images/contribution-map.png" alt="contribution-map" width="180">](https://github.com/pingcap/tidb-map/blob/master/maps/contribution-map.md#tikv-distributed-transactional-key-value-database)
 
 ## Building and setting up a development workspace