Add more detail to fork failure message

api/queries_repo.go

@@ -548,7 +548,7 @@ func ForkRepo(client *Client, repo ghrepo.Interface, org, newName string, defaul
 	// The GitHub API will happily return a HTTP 200 when attempting to fork own repo even though no forking
 	// actually took place. Ensure that we raise an error instead.
 	if ghrepo.IsSame(repo, newRepo) {
-		return newRepo, fmt.Errorf("%s cannot be forked", ghrepo.FullName(repo))
+		return newRepo, fmt.Errorf("%s cannot be forked to same owner or organization", ghrepo.FullName(repo))
 	}
 
 	return newRepo, nil