doc: clarify release candidate stability index

doc: clarify release candidate stability index · nodejs/node@95e9cab

Original file line number	Diff line number	Diff line change
`@@ -41,9 +41,9 @@ The stability indexes are as follows:`
`41`	`41`	`> minimum viability.`
`42`	`42`	`> * 1.2 - Release candidate. Experimental features at this stage are hopefully`
`43`	`43`	`> ready to become stable. No further breaking changes are anticipated but may`
`44`		`-> still occur in response to user feedback. We encourage user testing and`
`45`		`-> feedback so that we can know that this feature is ready to be marked as`
`46`		`-> stable.`
	`44`	`+> still occur in response to user feedback or the features' underlying`
	`45`	`+> specification development. We encourage user testing and feedback so that`
	`46`	`+> we can know that this feature is ready to be marked as stable.`
`47`	`47`	`>`
`48`	`48`	`> Experimental features leave the experimental status typically either by`
`49`	`49`	`> graduating to stable, or are removed without a deprecation cycle.`