Document file upload and download

Author: DivineOmega

README.md

@@ -36,4 +36,7 @@ $command = $connection->run('echo "Hello world!"');
 
 $command->getOutput();  // 'Hello World'
 $command->getError();   // ''
+
+$connection->upload($localPath, $remotePath);
+$connection->download($remotPath, $localPath);
 ```