Relay compiler --watch and yarn start

It is a little bit strange, that I need to run `yarn relay` on each iteration or run the watch process in another tab. So, I made such start command:

`node ./setup && concurrently \"PORT=4000 react-scripts start\" \"relay-compiler --src ./src --schema ./src/schema.graphql --watch\"`

Is this a good way? And should I create PR?

Start by comparing the existing `yarn relay` and `yarn start` workflow with the proposed command, using `./setup`, `./src`, and `./src/schema.graphql` as the mentioned entry points. Done means deciding whether one start command should run the React and Relay watch processes together and defining the project change needed.

Written by the indexing model from the issue text.