[Groff] Introduction to groff in french

[Grégoire Babey]

Hi groffies,

thanks again for your feedbacks. 
I wrote a second version for the introducion to groff in french. 
I splitted general presentation https://doc.ubuntu-fr.org/groff and
user tutorial https://doc.ubuntu-fr.org/groff_tuto


Cheers
Grégoire