update godoc and add MAINTAINERS for mflags

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)
Fix spelling of benchmark test

Docker-DCO-1.1-Signed-off-by: Paul Nasrat <pnasrat@gmail.com> (github: pnasrat)
Merge pull request #4672 from vieux/update_godoc_mflags

update godoc and add MAINTAINERS for mflags
Merge pull request #4686 from pnasrat/benchmark-typo

Fix spelling of benchmark test