Update documents fix drop column support features (#3628)
Update documents fix drop column support features (#3628)

* Update documents fix drop column support features

* Fix grama

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