Currently, in order to get a commit from an externally hosted repository to appear in a project's activity feed, the commit message must include the project's hashtag. For object rule triggers for commits, it would be nice if Herald had an option under "Take these actions every time this rule matches" called something like "Associate to project" or "Add to project feed." The current "Add emails to CC" action is not quite right in the sense that it results in the commit showing that project's name as a Subscriber, but that is all. The project does not show up under "Projects" and if you go to the project's activity feed, then you do not see the commit there.
For extra credit, it would be good to include under "When all of these conditions are met" an option to specify the branch on which the commit appears. That would allow associating multiple projects to the same repository based on the branch. For example, a maintenance project for stable updates on a separate branch from new development which might be on the master branch.