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.
"the students" = plural? "the students'" = all of them? or "a student's" just one?

If this course is the one that should be taken first, should it be ordered first in the introductory sentence and list?