Clarify that schema options can be applied at the schema level or global...

... level and some at the editor instance level.

Not sure if it was deliberate that `hidden` was not allowed on editor instances, but I thought the README ought to follow the pattern in the other sections and mention the possibility of using at least two of the options on the editor instance (even though I know the options are also documented there).

I also thought it should be clarified that the options could be placed on the schema.