Emphasize that blank node property lists cannot use `id`

[VladimirAlexiev]

https://w3c.github.io/N3/spec/#bnodeprplist gives an example, then a note:

See also the IRI property list syntax.

Being the busybody that I am, I tried to combine the two:

@prefix ex: <http://example.org/#> .

ex:john ex:address [
  ex:street "Evergreen Terrace" ;
  ex:number 742 ;
  ex:town [id _:springfield ex:name "Springfield" ]
] .

ex:john ex:address [ex:town _:springfield].

But it's not allowed to use id with a blank node name. So I think change the above note to:

Compare to the IRI property list syntax. Note: you cannot use that syntax (the id keyword) with blank node identifiers.

[william-vw]

Unsure how many people would think of this :-) Feel free to make a PR so others can give their thoughts.