Document how the baseURL works

Hi, I recently setup a site by forking this project and using hugo and gitlab pages https://gitlab.com/andyedison/andyedison.gitlab.io

One of the sticking points I had was while running locally, the CSS and javascript all worked. But after following the directions and making the site live, none of the CSS/Javascript/Images got 404's. After trying a lot of different things, what ended up doing the trick was editing the .gitlab-ci.yml file to add the --baseURL parameter to the hugo command:

- hugo --baseURL https://andyedison.gitlab.io

I had to do this even though I had the baseURL configured correctly inside the hugo config.toml

What I would like to know, is if you would accept a PR with a note added under the troubleshooting section of the README.md suggesting trying that option? Could save the next person some time.

Thanks very much for this great project. It is a really easy way to get a slick looking site up and running.