Document buildgrid threading
Adds this diagram: https://buildgrid.gitlab.io/-/buildgrid/-/jobs/359040200/artifacts/documentation/architecture_overview.html
Addresses: #217 (closed)
Edited by Marios Hadjimichael
Adds this diagram: https://buildgrid.gitlab.io/-/buildgrid/-/jobs/359040200/artifacts/documentation/architecture_overview.html
Addresses: #217 (closed)