document that to effectively add to suffixes you have to add to suffix_acronyms

[gvelez17]

So it took me a long time to understand why

nameparser.config.CONSTANTS.suffixes.add('pc')

was not effective, finally realized by reading the code that

nameparser.config.CONSTANTS.suffix_acronyms.add('pc')

would be, but it was not obvious. Maybe add this to the docs.

[derek73]

I've been burnt by this myself. When I originally split suffixes up in to different types I didn't even realize that CONSTANTS.suffixes is no longer hooked up to anything. I removed the documentation for suffixes but I think I need to just remove it entirely.