Add an Explainer and Reference section to the ReadMe on VID labelling process

[TNATALI]

Documentation request:
Currently there is very little information on the VID labelling process and reference material that can assist a new EDP to understand the VID Labelling process.
Suggestion is to add an easy to understand process and reference links to the README page on the virtual people server repo
https://github.com/world-federation-of-advertisers/virtual-people-core-serving/

Who will benefit: New EDPs and their technical team, New Markets, Tech team(s)