Warn user that commands are being run in another directory

src/Composer/Command/GlobalCommand.php

@@ -72,6 +72,7 @@ EOT
         // change to global dir
         $config = Factory::createConfig();
         chdir($config->get('home'));
+        $output->writeln('<info>Changed current directory to '.$config->get('home').'</info>');
 
         // create new input without "global" command prefix
         $input = new StringInput(preg_replace('{\bg(?:l(?:o(?:b(?:a(?:l)?)?)?)?)?\b}', '', $input->__toString(), 1));