Add Doxygen build instructions to docs/README.md (#416) #2560

Job	Run time
clang-format	9s
python-lint	11s
ubuntu-gcc-build (ubuntu-24.04)	1m 22s
ubuntu-gcc-build (ubuntu-24.04-arm)	2m 23s
ubuntu-clang-build (ubuntu-24.04)	1m 0s
windows-msvc-build	3m 15s
macos-clang-build	2m 24s
windows-clang-build	2m 51s
ubuntu-clang-build (ubuntu-24.04-arm)	3m 18s
windows-msvc-test	2m 12s
windows-clang-test	1m 27s
ubuntu-gcc-test (ubuntu-24.04)	4m 17s
ubuntu-gcc-test (ubuntu-24.04-arm)	4m 47s
ubuntu-clang-sanitizer-build (ubuntu-24.04)	1m 11s
ubuntu-clang-test (ubuntu-24.04)	4m 33s
ubuntu-clang-test (ubuntu-24.04-arm)	5m 49s
macos-clang-test	3m 13s
windows-msvc-test-extended	1m 21s
windows-clang-test-extended	1m 23s
macos-clang-test-extended	2m 21s
ubuntu-gcc-test-extended (ubuntu-24.04-arm)	3m 53s
ubuntu-gcc-test-extended (ubuntu-24.04)	2m 27s
ubuntu-clang-sanitizer-test (ubuntu-24.04)	1m 54s
ubuntu-clang-test-extended (ubuntu-24.04)	2m 43s
ubuntu-clang-test-extended (ubuntu-24.04-arm)	4m 6s
ubuntu-clang-sanitizer-test-extended (ubuntu-24.04)	1m 38s
ubuntu-gcc-build-codecov	3m 45s
ubuntu-gcc-build-perf-stats	1m 5s
	1h 10m 58s

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