VersionHistoryController should document its soft expectations

Updated the documentation for VersionHistoryController.

Looks good, but I'm not sure the @see links to specific entities is right here.

Yes true, with the @see links are entity-agnostic, rather we can have references to revision-related routes and interface

\Drupal\Core\Entity\Routing\RevisionHtmlRouteProvider
\Drupal\Core\Entity\RevisionableInterface

LGTM.

Thanks!