Update README.packetmill.md #662

Job	Run time
build (gcc, vanilla)	7m 34s
build (gcc, dpdk)	8m 16s
build (gcc, dpdk-light)	10m 19s
build (gcc, netmap)	7m 26s
build (gcc, vanilla-nopool)	7m 28s
build (gcc, dpdk-flow-dynamic)	8m 29s
build (clang, vanilla)	10m 43s
build (clang, dpdk)	11m 50s
build (clang, dpdk-light)	14m 13s
build (clang, netmap)	10m 59s
build (clang, vanilla-nopool)	10m 54s
build (clang, dpdk-flow-dynamic)	12m 18s
mirror	38s
	2h 1m 7s

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