Update docs

README.md

@@ -36,7 +36,14 @@ uglify(options);
 
 `options` - [uglifyJS API options](https://github.com/mishoo/UglifyJS2/blob/master/README.md#minify-options)
 
-`options.sourcemap` – default: `true`, type: `boolean`. The only own option which is used to generate source maps and pass them to rollup.
+`options.sourcemap: boolean`
+
+Generates source maps and passes them to rollup. Defaults to `true`.
+
+`options.numWorkers: number`
+
+Amount of workers to spawn. Defaults to the number of CPUs minus 1.
+
 
 ## Examples