README: Make cmake instructions more portable and simple #394

Job	Run time
linter	50s
windows (shared)	1m 11s
posix (linux, clang, shared)	13s
windows (static)	56s
posix (linux, clang, shared, ASan)	25s
posix (linux, clang, static)	21s
posix (linux, clang, static, ASan)	34s
posix (linux, gcc, shared)	16s
posix (linux, gcc, shared, ASan)	32s
posix (linux, gcc, static)	10s
posix (linux, gcc, static, ASan)	19s
posix (macos, clang, shared)	55s
posix (macos, clang, static)	11s
posix (macos, clang, static, ASan)	52s
	7m 45s

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