Sylvia/docs/doc 1105

@lamagnifica @catong @mhoeber: This is a draft of the updates to the Register Your Account section to reflect the new login/registration page. The feature is currently in a/b testing, so we don't want to merge the branch yet, but feedback is still welcome.
I'm wondering what value repeating the message text here has. The essential part is that they know that they have to go look for the email and respond to its instructions. 
If we're afraid people's spam filters will block the activation message, we should give the "from" email address here. Possibly, that's all that's needed.