Add tidb-backend necessary instructions (#4939)
Add tidb-backend necessary instructions (#4939)

* Update migrate-from-mysql-dumpling-files.md

* Apply suggestions from code review

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