sysvar: add description in INSTANCE sysvars (#10845)
sysvar: add description in INSTANCE sysvars (#10845)

* sysvar: add description in INSTANCE sysvars

* Fix

* Update system-variables.md

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

* Fix

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