thorium: add perf documentation

Changes from yesterday (with perf) lowered the running time
from 3min15s to 2m16.985s.

Link: https://github.com/GeneAssembly/biosal/issues/720
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
thorium: use lockless workers and lockless actors

Link: https://github.com/GeneAssembly/biosal/issues/720
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>