build

doc: add how to use the CI containers to build #3496

Job	Run time
default (gcc, release)	52s
default (clang, debug)	47s
cross (s390x)	56s
default (gcc, debug)	51s
default (clang, release)	59s
cross (armhf)	48s
muon minimal static	35s
cross (ppc64le)	49s
build libnvme and nvme-cli separately	43s
make static	40s
fallback shared libraries	0s
	8m 0s

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