Ensure the triple annotation example is useful

[niklasl]

In #16, concerns about the usefulness of the annotation example were raised. I believe at least some of them have been addressed and that we have enough agreement to merge. This issue is for resolving possible remaining concerns, including:

• Should another relationship be annotated instead?
• The choice of <is interested in>, one of the main relations in the already existing Primer example was deliberate. does changing the target of the annotation also mean that the basic example of the primer isn't good enough?
• If we do keep <is interested in> as the basis for the annotation), is the <Interest>, or maybe <Personal_interest>, a good enough example of a reification of that relationship? (Also see the choice of specific, well-known vocabularies used to encode this information in the Turtle section.)
• We need references to important concepts in RDF Concepts (especially to the concept of that triple terms denote, once that has been added).
• Other concerns regarding explanation and general wording.