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Docs: point remaining copy at main now that the experiment branch is … #159

Job	Run time
macOS host (SwiftUI build)	11m 10s
Windows host (WinRT build)	3m 45s
Contract preflight (i18n + release metadata)	4s
Linux host (GTK4 build)	1m 47s
Racket core (contract tests)	41s
	17m 27s