Refine RNTester documentation to disable fabric
Refine RNTester documentation to disable fabric

Summary:
Changelog: [Internal] Update the documentation to disable fabric in RN Tester.

RNTester build would fail if you previously built with fabric_enabled. This documentation adds the instruction to clean up before runing pod install.

In the future, we'd want to detect and do the clean up so that it doesn't fail in an obscure way.

Reviewed By: cortinico, dmitryrykun

Differential Revision: D33173173

fbshipit-source-id: a396eb71edc7bf174d0eb392799f45ae74274b76

janicduplessis/react-native,facebook/react-native,facebook/react-native,facebook/react-native,janicduplessis/react-native,janicduplessis/react-native,facebook/react-native,javache/react-native,javache/react-native,facebook/react-native,janicduplessis/react-native,javache/react-native,facebook/react-native,javache/react-native,javache/react-native,facebook/react-native,janicduplessis/react-native,javache/react-native,janicduplessis/react-native,javache/react-native,facebook/react-native,janicduplessis/react-native,javache/react-native,facebook/react-native,janicduplessis/react-native,javache/react-native