Readme.md and XOR assignment - preferredName()

My first pull request.  Everything look good?
Hi Hank,

Did you look at this closely?  There will never be TWO strings to concat.  There will be one, or the other, but not both... as per my comments.

This code was tested before I turned it in.  And it does work in the current setup.  

However, if it is bad form, or not good for any other reason, please do let me know?  Maybe it's confusing because it LOOKS like there is a concat going on?