Consider adding link to build setting documentation that Xcode now adds to its config file header comment

[dempseyatgithub]

Would need to double check that the URL is valid over time - Apple docs have a habit of dead links.

[dempseyatgithub]

Maybe instead of adding the link to the generated files themselves, since there is a good possibility of the URL going stale after a period of time, add the link to the project README instead.