how-to: add placement rule guide (#2171)#2810

Merged

TomShawn merged 4 commits intopingcap:release-3.1from sre-bot:release-3.1-e93c59582d7f

Jun 16, 2020

+354

Commits on Jun 11, 2020

cherry pick pingcap#2171 to release-3.1

TomShawn
authored and
sre-bot
committed

Commits on Jun 16, 2020