Added a simple README.md. #5

Job	Run time
Build (qemu_x86_defconfig, glibc)	28m 30s
Build (qemu_x86_defconfig, uclibc)	28m 33s
Build (qemu_x86_defconfig, musl)	28m 29s
Build (qemu_x86_64_defconfig, glibc)	28m 29s
Build (qemu_x86_64_defconfig, uclibc)	28m 29s
Build (qemu_x86_64_defconfig, musl)	28m 29s
Build (raspberrypi4_defconfig, glibc)	28m 33s
Build (raspberrypi4_defconfig, uclibc)	1s
Build (raspberrypi4_defconfig, musl)	28m 11s
Build (raspberrypi4_64_defconfig, glibc)	33m 12s
Build (raspberrypi4_64_defconfig, uclibc)	28m 29s
Build (raspberrypi4_64_defconfig, musl)	28m 10s
Build (qemu_ppc64le_pseries_defconfig, glibc)	28m 31s
Build (qemu_ppc64le_pseries_defconfig, uclibc)	28m 29s
Build (qemu_ppc64le_pseries_defconfig, musl)	28m 31s
Build (qemu_mips32r2_malta_defconfig, glibc)	28m 32s
Build (qemu_mips32r2_malta_defconfig, uclibc)	28m 49s
Build (qemu_mips32r2_malta_defconfig, musl)	28m 43s
Build (qemu_mips64_malta_defconfig, glibc)	28m 34s
Build (qemu_mips64_malta_defconfig, uclibc)	28m 32s
Build (qemu_mips64_malta_defconfig, musl)	28m 32s
	9h 34m 48s

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