Add a note about protocol limitations being driven by primitives such as URLs

[dlongley]

See conversation here: #26 (comment)

[msporny]

The group discussed this on the 2024-07-23 telecon:

For the interaction field in a VPR it was noted that if a protocol is to use a URL that using long URLs or stuffing many variables into a URL can be problematic because URLs tend to have length limitations in a variety of implementations. If a protocol requires many parameters in order to work, it is suggested that implementers should keep things encapsulated to the greatest extent that you can. So, 1) don't use long URLs, and 2) use short URLs and hide parameters behind URLs to the greatest extent possible, which will enable URLs to more easily travel through other mediums.

A PR should be raised that notes that values associated with the interaction property should use short URLs and place parameters "behind" the short URLs instead of exposing them in the interaction value.