reference: update TiFlash tune doc (#2642)
reference: update TiFlash tune doc (#2642)

* reference: update tiflash tune doc

* Update tune-performance.md

* Update reference/tiflash/tune-performance.md

Co-Authored-By: Keke Yi <4b13e11d5beb5669a80650bc9e0535372af5b679@users.noreply.github.com>

Co-authored-by: Soup <21499f78e176b473d4cd846847d53dfe587518c7@pingcap.com>
Co-authored-by: Keke Yi <4b13e11d5beb5669a80650bc9e0535372af5b679@users.noreply.github.com>
pingcap/docs-cn,pingcap/docs-cn