swarm: Document rollback, failure threshold, and monitor flags
swarm: Document rollback, failure threshold, and monitor flags

These are new flags to service create/update being added in a Docker
engine PR.

Signed-off-by: Aaron Lehmann <8ecfc6017a87905413dcd7d63696a2a4c351b604@docker.com>

BSWANG/denverdino.github.io,BSWANG/denverdino.github.io,BSWANG/denverdino.github.io,BSWANG/denverdino.github.io,BSWANG/denverdino.github.io