Update documentation.
Update documentation.

Summary:
See #1018
Closes https://github.com/facebook/jest/pull/1019

Differential Revision: D3315562

fbshipit-source-id: 349ce751573b01a0d793e53bf6caea71cff8c73c

mpontus/jest,blainekasten/jest,alvinsj/jest,sampepose/jest,razh/jest,aaron-goshine/jest,ide/jest,bookman25/jest,Daniel15/jest,mpontus/jest,blainekasten/jest,alvinsj/jest,Daniel15/jest,facebook/jest,cpojer/jest,sampepose/jest,bookman25/jest,skovhus/jest,ide/jest,blainekasten/jest,mpontus/jest,razh/jest,facebook/jest,Daniel15/jest,skovhus/jest,aaron-goshine/jest,ide/jest,cpojer/jest,bookman25/jest,skovhus/jest,cpojer/jest,aaron-goshine/jest,facebook/jest