Add info about about skeleton and website-skeleton?

[uikolas]

What about adding some info in: https://symfony.com/doc/master/setup.html about differences symfony/website-skeleton and symfony/skeleton ?
It's only mentioned in blog whats the difference between them: https://symfony.com/blog/the-end-of-the-symfony-standard-edition
Maybe it will be usefull for new users to choose what they really need?

[javiereguiluz]

Fixed by #9444. We now use the website-skeleton by default, but also mention the skeleton alternative in the main installation article.