Add "Tips for collection-holders" and "Tips for product developers" subsections

[nevali]

In each of the sections describing the different kinds of entities we have recommended approaches for, we should add a hints/tips section for both collection-holders and product developers containing any relevant salient advice relating to that particular class of thing.

[r4isstatic]

Yes - clear 'how do I' type things would be very good to have.

We're getting questions from potential product developers like:

"How do I access the actual media associated with things in RES?" - although in many cases this may be beyond our control, we should have a helpful answer for them ;)