In XCode 5, turn on 80-column line guide

Problem:

I am using XCode 5 and the coding style guide that I am using requires avoiding lines going past the 80-column mark, if possible.

How do I turn on the 80-column guide?

Solution:

1. Go to the XCode Preferences (in the menu: XCode -> Preferences...)
2. Go to the Text Editing tab
3. Check "Page guide at column: "
4. Change the number to 80, or to whatever column your required style guide needs