📝 Documentation: Clarify supported TypeScript version range

[JoshuaKGoldberg]

Bug Report Checklist

• I have pulled the latest main branch of the repository.
• I have searched for related issues and found none that matched my issue.

Overview

Neither the README.md nor https://joshuakgoldberg.github.io/ts-api-utils/stable/ mention what the supported versions of TypeScript are. We should really make that clear:

• Consumers shouldn't be surprised if their relatively old TS version doesn't work with ts-api-utils
• Dependents of ts-api-utils might have their own support ranges, and need to know if they match up

Per package.json, currently it's >=4.8.4:

ts-api-utils/package.json

Lines 95 to 97 in 0bd7d7a

	"peerDependencies": {
	"typescript": ">=4.8.4"
	},

Additional Info

Relevant to #711, which is on a feature not supported in older TS versions.

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