docs(gettingStarted): add Yarn install (#3588)
docs(gettingStarted): add Yarn install (#3588)

* docs(gettingStarted): add Yarn install

cc @cpojer

* Update GettingStarted.md

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