Clarify valueShape description

[kcoyle]

The primer does not say that a row with valueShape will not have a valueDataType. Isn't that the case? And the sentences under the table in that section seem unclear:

this TAP states that there must be at least one dct:creator and that this statement template links to the authorShape; that there must be one and only one dct:publisher, linked to the publisherShape. These shapes also have properties, and those properties can be constrained within the shape, such as with value types and cardinality.

I suggest dropping the last sentence.