4181 - Update claim page to include explanatory text for logged in users

Update the text on the page where creators can claim their works.

https://code.google.com/p/otwarchive/issues/detail?id=4181
I'm going to leave this comment on the issue, too, but this text makes some assumptions about how the user is accessing the page. Can we make this either "Select the following button" or "Use the following button" rather than "click on the button below?" (We'd normally say "Select $TextOfButton," but that is a bit unwieldy here.)