providers: Add chapril.org

I'm Adrien Bourmault, co-administrator of Chapril's XMPP service, a project which goal is to be an alternative to GAFAM, led by the April (the FSF's sister organization in France, for the promotion and defense of free software).

I've done here with the help of your readme the addition of chapril.org in your repository. Would you agree to add it in your list? Do not hesitate to ask me any additional question if I had forgotten any information, thank you !