Fix reference to the plugin in the README

Author: Andarist

README.md

@@ -189,7 +189,7 @@ export default babel.custom(babelCore => {
 		result(result, { code, customOptions, config, transformOptions }) {
 			return {
 				...result,
-				code: result.code + '\n// Generated by some custom loader',
+				code: result.code + '\n// Generated by some custom plugin',
 			};
 		},
 	};