Yay! I figured out how to follow Flipboard users on Friendica! I don't go to their profile, where I would need to sign up with a Flipboard account. I just search for them on Friendica, click on the result, and then press "follow". The rest is as always, where I can choose the channel, etc. Now, I can follow all sorts of accounts that I followed on Facebook and make my timeline a much happier place, full of interesting things!