Add explainer text for confirming new entries in user upload process

[emilyhopkins]

From Cory:

There should be some instructions on the upload forms telling me that
I add something not already there I have to wait a moment for Create...
to appear, and then select that. It's fine to do it this way, but people
are going to miss it is easily if they're not told, and think that it
doesn't work.