README: update istructions to add a FAQ entry

The instructions for the FAQ were not updated for the structure of the multilingual website. Adding updated instructions, but i'm considering to remove the step-by-step guides from the README.

Beside the fact that all those instructions are outdated or suggest to use now obsolete commands (like jekyll serve instead of bundle exec jekyll serve). I don't think it worth to spend the required time and efforts to keep those mini-guides updated. Especially now that many things are changing. Beside, since getmonero became multilingual, its complexity increased a lot and would be very hard for an user not familiar with jekyll to make a correct merge request and test it before submitting it.

I will trim the readme soon.