Docs: french translation

[nlaurance]

WIP at https://github.com/nlaurance/pgzero-french

[lordmauve]

@madbrain's fork has made a fair bit of progress on this: https://github.com/madbrain/pgzero-french

[madbrain]

We are working on it with @nlaurance to deliver the best quality translation :-)
There is still a great amount of work : next focus will be on API description and installation.

[madbrain]

I have just published on read the docs, a version of the translation :

https://pgzero-french.readthedocs.io/fr/latest/index.html

it's about 85% complete and certainly need some refinements here and there, but it's on a good way !