fix: increase header level for readme items #822

Job	Run time
js-test-and-release / check	1m 44s
js-test-and-release / test-firefox	40s
js-test-and-release / test-chrome	55s
js-test-and-release / test-chrome-webworker	42s
js-test-and-release / test-node (windows-latest, lts/*)	6m 29s
js-test-and-release / test-electron-main	35s
js-test-and-release / test-node (ubuntu-latest, lts/*)	3m 33s
js-test-and-release / test-node (macos-latest, lts/*)	4m 35s
js-test-and-release / test-firefox-webworker	29s
js-test-and-release / test-webkit (ubuntu-latest, lts/*)	21s
js-test-and-release / test-webkit (macos-latest, lts/*)	1m 50s
js-test-and-release / test-webkit-webworker (ubuntu-latest, lts/*)	16s
js-test-and-release / test-webkit-webworker (macos-latest, lts/*)	2m 19s
js-test-and-release / test-electron-renderer	20s
js-test-and-release / release-check	0s
js-test-and-release / release	0s
	24m 48s

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