I'd expect the
<"a href ="/about-us"> to be more like
<"a href ="../about-us"> as that page may be a page up in the hierarchy. In any case, you'll want to verify it's location relative to where it's at in the footer on the pages you're using it with and make appropriate adjustments. It simply may not be pointing to the correct path which is the essence of the message you're receiving.
This may not be related to your issue, but I also know that from the Winter16 Release notes, you want to add
access=”global” to the inside of
<aura:component> to make your resource avail for installation outside your org. Whether a community is considered "outside your org" is another matter. I believe that notation is more for ISVs, but you might want to add it just the same.
Knowing that the link was a reference to a single page application would have been helpful. Your link needs to point to the part of your code that calls the "about us" page. Take a look at the SF1 Mobile App Developer Guide section on Navigation to see how to call those links to initiate that code. I think you want to be using either
navigateToURL instead. Which to use would depend on the rest of your code.