Replace the Flow documentation section (facebook#1245)

Author: gaearon

packages/react-scripts/template/README.md

@@ -445,28 +445,21 @@ Now you are ready to use the imported React Bootstrap components within your com
 
 ## Adding Flow
 
-Flow typing is currently [not supported out of the box](https://github.com/facebookincubator/create-react-app/issues/72) with the default `.flowconfig` generated by Flow. If you run it, you might get errors like this:
+Flow is a static type checker that helps you write code with fewer bugs. Check out this [introduction to using static types in JavaScript](https://medium.com/@preethikasireddy/why-use-static-types-in-javascript-part-1-8382da1e0adb) if you are new to this concept.
 
-```js
-node_modules/fbjs/lib/Deferred.js.flow:60
- 60:     Promise.prototype.done.apply(this._promise, arguments);
-                           ^^^^ property `done`. Property not found in
-495: declare class Promise<+R> {
-     ^ Promise. See lib: /private/tmp/flow/flowlib_34952d31/core.js:495
+Recent versions of [Flow](http://flowtype.org/) work with Create React App projects out of the box. 
 
-node_modules/fbjs/lib/shallowEqual.js.flow:29
- 29:     return x !== 0 || 1 / (x: $FlowIssue) === 1 / (y: $FlowIssue);
-                                   ^^^^^^^^^^ identifier `$FlowIssue`. Could not resolve name
-```
+To add Flow to a Create React App project, follow these steps:
 
-To fix this, change your `.flowconfig` to look like this:
+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`).
 
-```ini
-[ignore]
-<PROJECT_ROOT>/node_modules/fbjs/.*
-```
+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.
+In the future we plan to integrate it into Create React App even more closely.
 
-Re-run flow, and you shouldn’t get any extra issues.
+To learn more about Flow, check out [its documentation](https://flowtype.org/).
 
 ## Adding Custom Environment Variables