Minor README cleanup #2017

Job	Run time
Generate semantic release version using git-describe-semver	5s
Build oldstable Alpine x86 image using Makefile	56s
Build stable Alpine x64 image using Makefile	58s
Build oldstable Alpine x64 image using Makefile	57s
Build stable Alpine x86 image using Makefile	1m 13s
Build oldstable cgo-mingw-w64 x64 image using Makefile	1m 24s
Build oldstable cgo-mingw-w64 x86 image using Makefile	1m 30s
Build stable image using Makefile	1m 38s
Build stable cgo-mingw-w64 x64 image using Makefile	1m 45s
Build stable cgo-mingw-w64 x86 image using Makefile	1m 41s
Build unstable Alpine x64 image using Makefile	51s
Build unstable Alpine x86 image using Makefile	1m 15s
Build unstable cgo-mingw-w64 x64 image using Makefile	1m 24s
Build unstable cgo-mingw-w64 x86 image using Makefile	1m 34s
Build oldstable image using Makefile	1m 46s
Build stable mirror images using Makefile	36s
Build unstable image using Makefile	2m 26s
	21m 59s

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