readme: add description of ECMAScript #138

Job	Run time
tests / build	10s
tests / build	10s
tests / matrix	9s
tests / matrix	9s
tests / latest minors (9.11)	2m 58s
tests / latest minors (9.11)	2m 58s
tests / latest minors (8.17)	5m 34s
tests / latest minors (8.17)	1s
tests / latest minors (7.10)	1m 4s
tests / latest minors (7.10)	1m 4s
tests / latest minors (6.17)	1m 15s
tests / latest minors (6.17)	1m 15s
tests / latest minors (5.12)	1m 33s
tests / latest minors (5.12)	1m 33s
tests / latest minors (4.9)	49s
tests / latest minors (4.9)	49s
tests / latest minors (3.3)	1m 1s
tests / latest minors (3.3)	1m 1s
tests / latest minors (2.5)	1m 4s
tests / latest minors (2.5)	1m 4s
tests / latest minors (1.8)	59s
tests / latest minors (1.8)	59s
tests / latest minors (0.12)	1m 10s
tests / latest minors (0.12)	1m 10s
tests / latest minors (0.10)	1m 13s
tests / latest minors (0.10)	1m 13s
tests / latest minors (0.8)	1m 10s
tests / latest minors (0.8)	1m 10s
tests / non-latest minors	0s
tests / non-latest minors	1s
tests / node ${{ inputs.type }} @ ${{ inputs.range }}	0s
tests / node ${{ inputs.type }} @ ${{ inputs.range }}	1s
	34m 47s

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