Update tidb-lightning-overview.md (#3764)
Update tidb-lightning-overview.md (#3764)

* Update tidb-lightning-overview.md

* Update tidb-lightning-overview.md

* Update tidb-lightning/tidb-lightning-overview.md

Co-authored-by: TomShawn <3d0966147538bc5ab020e8dffa2c0b746f9728a6@users.noreply.github.com>
pingcap/docs,pingcap/docs,pingcap/docs