uploads gdoc content for building mocks

Why

Need to have documentation for how/why users can build mocks

Documents where to retrieve the information users will use when building mocks.

This is been through tech writer review.

n/a

This will be reflected on the changelog (commit following shortly).

[y] I have checked if any docs change here also requires updates to other repositories (ADRs / RFCs, README.md, Team Manual, elsewhere in these docs)
[y] Where there is any overlap I have updated or opened a PR for corresponding changes