This is a good idea. Also, we can use the 'help-wanted' tag, too, and that is synced with Code for America's Civic Tech Issue Finder.
Also, depending on the size of the task, you (and anyone else who authenticates with GitHUb, should have the ability to create new blog posts to announce tasks as well.
That would be a good means to broaden the announcement. Maybe the Facebook group as well? I'm not sure what your full media strategy is.
Recorded a quick screencast for those unfamiliar to GitHub showing how to make a contribution to the Task Basket or any GH repo, for that matter:
That may be more of @josefrs or @apompei question, Roy, but I see Facebook more as a tool to bring in people from outside of the established community, not so much as a project management notification/announcement place. But that's just my quick initial take.