Add links with more info to help drawers

[mplorentz]

Our help drawers (#740) provide some good basic info about each of our main screens, but I think it would be good to have links to Zendesk or our wiki or something for people who want to learn more, or who tapped the help button for some specific reason that wasn't covered in the drawer text.

[mplorentz]

Also specifically consider adding a link to the word "gossip" on the Your Network drawer re: https://github.com/planetary-social/planetary-ios/pull/740#pullrequestreview-1047965767

[rabble]

Needs somebody to write those documents.