explain: add indexes (#4913)
explain: add indexes (#4913)

* explain: add indexes

* Update explain-indexes.md

* Apply suggestions from code review

Co-authored-by: Keke Yi <4b13e11d5beb5669a80650bc9e0535372af5b679@users.noreply.github.com>

Co-authored-by: Keke Yi <4b13e11d5beb5669a80650bc9e0535372af5b679@users.noreply.github.com>
pingcap/docs-cn,pingcap/docs-cn