Minor French Update + NiceHash guide re-re-added

Created by: el00ruobuob

This is a small update for fr.yml on which some sentences were missing translation since relocalization (why in hell didn't i see that before??) This try (another time) to add the nicehash guide "How to mine Monero XMR without a mining equipement" which has always been here, but never been accessible through user-guide index page.