There isn't currently a user guide for 4.0, but we'll link to it in the app once we have one. The forums are linked from the About screen (bottom of Settings).
We're not allowed to link to the store at the moment - even in a beta - due to Apple's App Store Review Guidelines forbidding us from doing that. However, there's currently a court order in California requiring Apple to let developers link to their stores - Apple is (in my opinion) not really complying with it (you can do it but there's a scary warning screen and you have to pay the the same commission that you'd pay with the App Store), but the other party in the lawsuit is pushing back against that, so if the judge rules against Apple, we will duly add that link. (and probably also offer + advertise lower pricing for add-ons bought through our store)