NPM version check for tip (facebook#1193)

* Implemented a version check of npm to give a soft tip during the install procedure
and fixed gitignore

* Moved NPM check to method, it is only executed when you use NPM and the version is < 3.

* Minor formatting tweaks

* Simplify the code

* Remove unnecessary change

.gitignore

@@ -1,3 +1,5 @@
+.idea/
+.vscode/
 node_modules/
 build
 .DS_Store

packages/create-react-app/index.js

@@ -152,6 +152,7 @@ function install(dependencies, verbose, callback) {
     command = 'yarnpkg';
     args = [ 'add', '--exact'].concat(dependencies);
   } else {
+    checkNpmVersion();
     command = 'npm';
     args = ['install', '--save', '--save-exact'].concat(dependencies);
   }
@@ -173,7 +174,10 @@ function run(root, appName, version, verbose, originalDirectory, template) {
   var allDependencies = ['react', 'react-dom', packageToInstall];
 
   console.log('Installing packages. This might take a couple minutes.');
-  console.log('Installing ' + chalk.cyan('react, react-dom, ' + packageName) + '...');
+  console.log(
+    'Installing ' + chalk.cyan('react') + ', ' + chalk.cyan('react-dom') +
+    ', and ' + chalk.cyan(packageName) + '...'
+  );
   console.log();
 
   install(allDependencies, verbose, function(code, command, args) {
@@ -230,6 +234,25 @@ function getPackageName(installPackage) {
   return installPackage;
 }
 
+function checkNpmVersion() {
+  var isNpm2 = false;
+  try {
+    var npmVersion = execSync('npm --version').toString();
+    isNpm2 = semver.lt(npmVersion, '3.0.0');
+  } catch (err) {
+    return;
+  }
+  if (!isNpm2) {
+    return;
+  }
+  console.log(chalk.yellow('It looks like you are using npm 2.'));
+  console.log(chalk.yellow(
+    'We suggest using npm 3 or Yarn for faster install times ' +
+    'and less disk space usage.'
+  ));
+  console.log();
+}
+
 function checkNodeVersion(packageName) {
   var packageJsonPath = path.resolve(
     process.cwd(),