Added a simple README.md. #3

Job	Run time
Build (qemu_x86_defconfig, glibc)	27m 36s
Build (qemu_x86_defconfig, uclibc)	27m 39s
Build (qemu_x86_defconfig, musl)	27m 40s
Build (qemu_x86_64_defconfig, glibc)	27m 41s
Build (qemu_x86_64_defconfig, uclibc)	27m 40s
Build (qemu_x86_64_defconfig, musl)	27m 45s
Build (raspberrypi4_defconfig, glibc)	27m 35s
Build (raspberrypi4_defconfig, uclibc)	1s
Build (raspberrypi4_defconfig, musl)	27m 33s
Build (raspberrypi4_64_defconfig, glibc)	27m 39s
Build (raspberrypi4_64_defconfig, uclibc)	27m 21s
Build (raspberrypi4_64_defconfig, musl)	27m 39s
Build (qemu_ppc64le_pseries_defconfig, glibc)	27m 38s
Build (qemu_ppc64le_pseries_defconfig, uclibc)	27m 43s
Build (qemu_ppc64le_pseries_defconfig, musl)	27m 40s
Build (qemu_mips32r2_malta_defconfig, glibc)	27m 58s
Build (qemu_mips32r2_malta_defconfig, uclibc)	27m 43s
Build (qemu_mips32r2_malta_defconfig, musl)	27m 44s
Build (qemu_mips64_malta_defconfig, glibc)	27m 44s
Build (qemu_mips64_malta_defconfig, uclibc)	27m 39s
Build (qemu_mips64_malta_defconfig, musl)	27m 42s
	9h 13m 20s

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