chore: add a prettier config

.prettierrc.js

@@ -0,0 +1,15 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ */
+
+'use strict'
+
+module.exports = {
+  singleQuote: true,
+  trailingComma: 'es5',
+  semi: false,
+}