docs(README): add concurrent building in features section

README.md

@@ -19,6 +19,7 @@ Although NW.js has much lesser popularity than Electron, and is really troubled
   * Windows: `nsis`
   * macOS: TODO
   * Linux: TODO
+* Building for different platforms concurrently
 * Configurable executable fields and icons for Windows and macOS
 * Integration for `nwjs-ffmpeg-prebuilt`
 * Exclusion of useless files from `node_modules`