Git upgrade: Tweak README, bump version, fix a bug

Reviewed By: mkonicek

Differential Revision:
D4276644
Ninja: OSS only

fbshipit-source-id: 7bed331770d06addedf51e2ed09d0b9bde5b45ad

Author: Martin Konicek

react-native-git-upgrade/README.md

@@ -1,9 +1,17 @@
 # React Native Git Upgrade
 
-This tool make upgrading your apps to a new version of React Native easier than the stock `react-native upgrade` command.
+This tool makes upgrading your apps to a new version of React Native easier than the stock `react-native upgrade` command.
 
 It uses Git under the hood to automatically resolve merge conflicts in project templates (native iOS and Android files, `.flowconfig` etc.). These conflicts happen when a new React Native version introduces changes to those files and you have local changes in those files too, which is quite common situation.
 
 ## Usage
 
 See the [Upgrading docs](http://facebook.github.io/react-native/releases/next/docs/upgrading.html) on the React Native website.
+
+Simplest use case:
+
+```
+$ npm install -g react-native-git-upgrade
+$ cd MyReactNativeApp
+$ react-native-git-upgrade
+```

react-native-git-upgrade/package.json

@@ -1,6 +1,6 @@
 {
   "name": "react-native-git-upgrade",
-  "version": "0.1.0",
+  "version": "0.2.2",
   "license": "BSD-3-Clause",
   "description": "The React Native upgrade tool",
   "main": "cli.js",

react-native-git-upgrade/yarn.js

@@ -8,6 +8,7 @@
  */
 'use strict';
 
+const execSync = require('child_process').execSync;
 const fs = require('fs');
 const path = require('path');
 const semver = require('semver');