Support README.md in HTML help. #9573

Job	Run time
MacOS (macOS-15-intel)	51m 50s
Windows (check, intel)	52m 7s
MacOS (macOS-15)	28m 35s
Windows (installer, arm)	24m 49s
Windows (installer, intel)	23m 15s
Linux (clang, debian:stable, arm)	33m 36s
Linux (gcc, debian:stable, arm)	33m 53s
Linux (gcc, debian:stable, intel)	35m 42s
Linux (clang, debian:testing, intel)	34m 45s
Linux (clang, debian:stable, intel)	34m 34s
Linux (clang, debian:testing, arm)	32m 0s
Linux (gcc, debian:testing, arm)	34m 13s
Windows (check, arm)	51m 16s
Linux (gcc, debian:testing, intel)	34m 15s
	8h 24m 50s

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