Go to the "Link Binary with Libraries" option and click +. It's found on the Build Phases page of your main Xcode project settings. You might want to collapse the Target Dependency and Compile Sources sections, so that the Link Binaries section is fully visible on your screen.
Footnote:
My mistake was clicking "+" in the Target Dependencies section, which was where I thought I might "add a dependency on CoreFoundation", which isn't what you do. I also found it confusing that you Link Binary with Libraries, when I thought that Xcode didn't use Framework and Library terms interchangeably, and in this case, confusingly. It also doesn't help that the plus icon is hidden and you have to scroll to access it, or else collapse the two top sections. Xcode is full of "User Interface is very confusing" areas, in my opinion:
Also, add #import <CoreFoundation/CoreFoundation.h>
to your implementation (.m) files, as needed.