Don't wait until the last step to tell new users they can only embed one file

OK that’s great. However the software had many opportunities to tell the user earlier,
and not at the very last step, causing the user to need to rewrite his article to allow it to make sense,
— even if he can add the other picture in a reply.

So please also check at this stage:

And even check here too:
in fact it can become even greyer, with a mouseover “Too many images in this edit already.”