Improve the consumer getting started for repos

[memsharded]

The next natural step that pure consumers want is to locate and install different packages from different repositories.

This is a bit hidden in the docs, maybe it would be good to extend the "getting started" section or in the next one, to introduce consumers to these cases.

[danimtb]

Agree. It could be included here: https://docs.conan.io/en/latest/using_packages.html