How do I install rEFInd on a MacBook running macOS Sierra?
After reading through the refind-install script (at version 0.10.4), I discovered that all I needed to do was make sure that the EFI partition was mounted.


From the terminal, run diskutil list to find the EFI partition. In my case this was /dev/disk0s1. 
Mount the EFI partition from the location identified in step 1. For me this was mount /dev/disk0s1
Run the rEFInd install script (from the unzipped rEFInd directory): sudo ./refind-install


I got friendly output in my terminal: Installation has completed successfully. After this rEFInd worked on my MacBook Pro.