In-App notice for launch of v17

[cstiens]

Before v17 is pushed to the app store, we will let users know that Orbot is getting a new look.

Here's a sketch. I'm thinking that we say 'Usability' updates instead of brand to put an emphasis on the fact that there are UX improvements. Overall, I want to keep the text here short. We could link out to an announcement blog post where we share more information about the changes and why Orbie was born.

[cstiens]

Here's a preview of the update app icon:

Assets are here: https://github.com/cstiens/orbot-apple/tree/main/docs