Specify what files are served form a bare local copy (facebook#8749)

Author: challet

CONTRIBUTING.md

@@ -94,7 +94,7 @@ All functionality must be retained (and configuration given to the user) if they
 
 2. Run `yarn` in the root `create-react-app` folder.
 
-Once it is done, you can modify any file locally and run `yarn start`, `yarn test` or `yarn build` like you can in a generated project.
+Once it is done, you can modify any file locally and run `yarn start`, `yarn test` or `yarn build` like you can in a generated project. It will serve the application from the files located in `packages/cra-template/template`.
 
 If you want to try out the end-to-end flow with the global CLI, you can do this too: