Document likely use of RegisterDynamicBackgroundWorker by another
background worker.
Reported-by: Chapman Flack
Discussion: https://postgr.es/m/CAB7nPqTdi=J9HH8PPPiEOohebdd+xkgbbhdY7=VbGnZ3CkZXxA@mail.gmail.com
Author: Chapman Flack
*worker, BackgroundWorkerHandle **handle). Unlike
RegisterBackgroundWorker, which can only be called from within
the postmaster, RegisterDynamicBackgroundWorker must be
- called from a regular backend.
+ called from a regular backend, possibly another background worker.