Add a place on the template that says website was made with OTTR template and can list authors

[kweav]

Like how the _output.yml file does with the course OTTR Template (below the table of contents): add a place that says this website was rendered using an OTTR Template and can list authors

[kweav]

@carriewright11 for branding consideration, could we easily make a footer.html that gets referenced in _site.yml?