Add Occitan language

[BoFFire]

Hello @Gargron,

Can you add Occitan language to both JoinMastodon Crowdin project and web ? I've discussed with a friend and he is ready to translate JoinMastodon to occitan.

Thank you 🥰 !

[BoFFire]

Related to https://github.com/mastodon/joinmastodon/pull/47

[Mejans]

Hello @Gargron and @BoFFire The translation is now 100%, can it be added to the website please? Best regards