Clarifying the docs about test.only (#5262)
Clarifying the docs about test.only (#5262)

* Clarifying the docs about test.only

It wasn't clear that test.only just applys to a single file.

* Update GlobalAPI.md

bookman25/jest,ide/jest,ide/jest,ide/jest,facebook/jest,facebook/jest,cpojer/jest,bookman25/jest,cpojer/jest,cpojer/jest,facebook/jest,bookman25/jest