Add Roadmap document and navigation link (#1373) #2276

Job	Run time
build (macos-latest, Release)	6m 24s
build (macos-latest, Debug)	9m 10s
build (ubuntu-latest, Debug)	6m 59s
build (windows-latest, Debug)	11m 17s
build (windows-latest, Release)	11m 40s
build (ubuntu-latest, Release)	6m 55s
publish-coverage / publish-coverage	1m 9s
	53m 34s

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