[DOCS] Example setup for multi-site/-locale instance

[aarongerig]

Q	A
Bug fix?	no
New feature?	no
BC breaks?	no
Deprecations?	yes/no

As promised, here's the documentation of an example setup of a multi-locale/multi-site Pimcore instance.
Any feedback/inputs are very appreciated! @benwalch @solverat

[solverat]

hey @aarongerig better late then never :) - could you please change the release from 2.0 to 3.0 (which we will release soon)?

Thanks!

[aarongerig]

@solverat Changed the release in the docs (composer require) to 3.0. I hope that's what you meant.

[solverat]

@aarongerig pefect! thank you!