Update flow configuration documentation (facebook#1518)

* Update flow configuration documentation

The documentation was missing creating the .flowconfig file

* Update flow configuration documentation

Adding in suggested changes

* Wording

* Wording

packages/react-scripts/template/README.md

@@ -585,7 +585,8 @@ To add Flow to a Create React App project, follow these steps:
 
 1. Run `npm install --save-dev flow-bin`.
 2. Add `"flow": "flow"` to the `scripts` section of your `package.json`.
-3. Add `// @flow` to any files you want to type check (for example, to `src/App.js`).
+3. Run `npm run flow -- init` to create a [`.flowconfig` file](https://flowtype.org/docs/advanced-configuration.html) in the root directory.
+4. Add `// @flow` to any files you want to type check (for example, to `src/App.js`).
 
 Now you can run `npm run flow` to check the files for type errors.
 You can optionally use an IDE like [Nuclide](https://nuclide.io/docs/languages/flow/) for a better integrated experience.