📚 Add RFC9051 link to README #1779

Job	Run time
ruby-versions / Generate Ruby versions	2s
build (3.1 / ubuntu-latest)	37s
build (3.1 / macos-latest)	23s
build (3.1 / windows-latest)	2m 0s
build (3.2 / ubuntu-latest)	41s
build (3.2 / macos-latest)	21s
build (3.2 / windows-latest)	2m 26s
build (3.3 / ubuntu-latest)	37s
build (3.3 / macos-latest)	27s
build (3.3 / windows-latest)	3m 39s
build (3.4 / ubuntu-latest)	38s
build (3.4 / macos-latest)	25s
build (3.4 / windows-latest)	2m 36s
build (head / ubuntu-latest)	43s
build (head / macos-latest)	24s
build (head / windows-latest)	1m 51s
	17m 50s

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