Add guideline for the info.documentation URL to point to the API's repository

[tanjadegroot]

Problem description
Today the URL in the info.documentation field is pointing to the overall CAMARA project.

Expected action
Update the info section in API design guidelines to specify that the URL should point to the API repository (which holds all documentation).

Can be done now or for Fall25 version.
it is recommended through the review for many APIs already.