update README with publicPath doc link

Author: shellscape

README.md

@@ -152,7 +152,9 @@ Type: `String`
 _Required_
 
 The public path that the middleware is bound to. _Best Practice: use the same
-`publicPath` defined in your webpack config._
+`publicPath` defined in your webpack config. For more information about
+`publicPath`, please see
+[the webpack documentation](https://webpack.js.org/guides/public-path)._
 
 ### reporter
 
@@ -399,4 +401,4 @@ We welcome your contributions! Please have a read of [CONTRIBUTING.md](CONTRIBUT
 [middleware-url]: https://github.com/webpack/webpack-dev-middleware
 [stack-url]: https://stackoverflow.com/questions/tagged/webpack-dev-middleware
 [uglify-url]: https://github.com/webpack-contrib/uglifyjs-webpack-plugin
-[wjo-url]: https://github.com/webpack/webpack.js.org
+[wjo-url]: https://github.com/webpack/webpack.js.org