Update tfjs-react-native README to add steps to fix a build error when using expo for web (#4805)
Update tfjs-react-native README to add steps to fix a build error when using expo for web (#4805)

DOC
* update

* Update README.md

Co-authored-by: Ping Yu <e3982a96662cc73e971d68f6aafe25f9d2e93e85@users.noreply.github.com>
tensorflow/tfjs,tensorflow/tfjs,tensorflow/tfjs,tensorflow/tfjs,tensorflow/tfjs,tensorflow/tfjs,tensorflow/tfjs,tensorflow/tfjs,tensorflow/tfjs