docs: Add footnote in main Readme #12

Job	Run time
test-code / test-fast (ubuntu)	59s
test-code / test-fast (windows)	32s
test-code / test-general (ubuntu, 3.8)	3m 28s
test-code / test-fast (macos)	2m 10s
test-code / test-general (ubuntu, 3.9)	3m 43s
test-code / test-general (ubuntu, 3.10)	3m 44s
test-code / test-general (ubuntu, 3.11)	3m 26s
test-code / test-general (ubuntu, 3.12)	3m 27s
test-code / test-general (windows, 3.8)	5m 55s
test-code / test-general (windows, 3.9)	6m 59s
test-code / test-general (windows, 3.10)	7m 8s
test-code / test-general (windows, 3.11)	5m 43s
test-code / test-general (windows, 3.12)	5m 45s
test-code / test-general (macos, 3.8)	5m 43s
test-code / test-general (macos, 3.9)	2m 37s
test-code / test-general (macos, 3.10)	2m 43s
test-code / test-general (macos, 3.11)	2m 20s
test-code / test-general (macos, 3.12)	2m 53s
test-code / Test Results	8s
test-code / check-tests-passed	3s
	1h 9m 26s

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