Revise FAQ entries for blueCFD-Core 2017 and 2020

[wyldckat]

Associated to the release of blueCFD-Core 2017, several FAQ entries will need to be revised, since new information is available.

This is somewhat also related to #76.

[wyldckat]

Currently this means revising this: https://github.com/blueCFD/Core/discussions/categories/q-a