Document `unnecessary-optional-chain` lint
Document `unnecessary-optional-chain` lint

Summary: Noticed this page exists, so I'm belatedly adding docs for the new lint

Reviewed By: gabelevi

Differential Revision: D8321328

fbshipit-source-id: c14b786303d528e79d64ed28428329c6449d37cf

gabelevi/flow,claudiopro/flow,popham/flow,mroch/flow,popham/flow,mroch/flow,JonathanUsername/flow,mroch/flow,JonathanUsername/flow,jamesgpearce/flow,jamesgpearce/flow,samwgoldman/flow,facebook/flow,jamesgpearce/flow,jamesgpearce/flow,AgentME/flow,gabelevi/flow,claudiopro/flow,mroch/flow,popham/flow,mroch/flow,claudiopro/flow,gabelevi/flow,samwgoldman/flow,AgentME/flow,JonathanUsername/flow,samwgoldman/flow,jamesgpearce/flow,nmote/flow,samwgoldman/flow,gabelevi/flow,facebook/flow,JonathanUsername/flow,claudiopro/flow,JonathanUsername/flow,nmote/flow,samwgoldman/flow,samwgoldman/flow,gabelevi/flow,nmote/flow,mroch/flow,facebook/flow,popham/flow,JonathanUsername/flow,nmote/flow,AgentME/flow,gabelevi/flow,nmote/flow,facebook/flow,nmote/flow,jamesgpearce/flow,JonathanUsername/flow,claudiopro/flow,popham/flow,jamesgpearce/flow,facebook/flow,facebook/flow,AgentME/flow,facebook/flow,samwgoldman/flow,mroch/flow,gabelevi/flow,AgentME/flow,popham/flow,popham/flow,nmote/flow