refine ecosystem tool guide document (#4627) (#4628)

* cherry pick #4627 to release-4.0

Signed-off-by: ti-srebot <ti-srebot@pingcap.com>

* Apply suggestions from code review

Co-authored-by: Chunzhu Li <lichunzhu@stu.xjtu.edu.cn>
Co-authored-by: TomShawn <41534398+TomShawn@users.noreply.github.com>

ecosystem-tool-user-guide.md

@@ -18,6 +18,10 @@ The following are the basics of Dumpling:
 - Supported TiDB versions: all versions
 - Kubernetes support: No
 
+> **Note:**
+>
+> PingCAP previously maintained a fork of the [mydumper project](https://github.com/maxbube/mydumper) with enhancements specific to TiDB. This fork has since been replaced by [Dumpling](/dumpling-overview.md), which has been rewritten in Go, and supports more optimizations that are specific to TiDB. It is strongly recommended that you use Dumpling instead of mydumper.
+
 ## Full data import
 
 [TiDB Lightning](/tidb-lightning/tidb-lightning-overview.md) (Lightning) is a tool used for the full import of large amounts of data into a TiDB cluster. Currently, TiDB Lightning supports reading SQL dump exported via Dumpling or CSV data source.