French translation of community/index.html
Force French links from French pages
Add back breadcrumbs
Merge pull request #422 from lefessan/docs-index.fr.md

Partial translation to French (2/3) of docs/index.md
Merge pull request #423 from lefessan/community-index.fr.md

French translation of community/index.html
Merge pull request #424 from lefessan/more-fr-links

Force French links from French pages
Remove main header newlines

The newlines were rendered as weird symbols on a smartphone.
Translate 2nd occurrence of "Edit this page"
Add a mailmap file
Add a contributors page

Fixes https://github.com/ocaml/ocaml.org/issues/420
Finish French translation of docs/index.fr.md