Create the .gitignore file as part of the installation

src/Symfony/Installer/NewCommand.php

@@ -61,6 +61,7 @@ protected function execute(InputInterface $input, OutputInterface $output)
             ->checkSymfonyVersionIsInstallable()
             ->download()
             ->extract()
+            ->createGitIgnore()
             ->cleanUp()
             ->checkSymfonyRequirements()
             ->displayInstallationResult()
@@ -275,6 +276,33 @@ private function extract()
         return $this;
     }
 
+    /**
+     * Creates the .gitignore file.
+     */
+    private function createGitIgnore()
+    {
+        $ignored = array(
+            '/web/bundles/',
+            '/app/bootstrap.php.cache',
+            '/app/cache/*',
+            '/app/config/parameters.yml',
+            '/app/logs/*',
+            '!app/cache/.gitkeep',
+            '!app/logs/.gitkeep',
+            '/app/phpunit.xml',
+            '/build/',
+            '/vendor/',
+            '/bin/',
+        );
+
+        $this->fs->dumpFile(
+            $this->projectDir.DIRECTORY_SEPARATOR.'.gitignore',
+            implode(PHP_EOL, $ignored).PHP_EOL
+        );
+
+        return $this;
+    }
+
     /**
      * Removes all the temporary files and directories created to
      * download and extract Symfony.