Clarified the port that is used by the internal web server in README
Added `sass` errors to console & `online` option in `serve` & `serve:dist`

I added the `errLogToConsole` in gulp-sass to avoid that watch stop working if an introduced modification does not compile. I also added the `online` options to `BrowserSync` to avoid that when no Internet connection the server needs 2 minutes to start to serve