Initial setup is confusing

[idimopoulos]

During a fresh installation, I tried to create a sample rdf bundle so I went on creating one without assigning all properties apart from the rdf_type, bundle predicate, title, owner, and created/changed mappings.
I was able to create an entity like this, but when I tried to edit it - without changing anything - I got the following error message

This kinda relates to the translations I think. I assigned all mappings and created a new entity which I was able to edit normally but I still couldn't edit the faulty ones.

Also, I think that in the creation form, we can add some descriptions to provide some ideas for default values on the mappings, like the created and changed dates, can be by default dates. The title, can be by default a translatable literal and so on, so that a new user can get a small idea of the type mappings.