More README info

README.md

@@ -1,6 +1,6 @@
 # Secret Santa Script
 
-This is a simple Ruby script for assigning secret Santas and emailing everyone their assignment.
+This is a simple Ruby script for assigning secret Santas and emailing everyone their assignment. The basic rule is that nobody can be assigned to give a gift to someone in their own group (including, of course, themselves). In my family, group == household, but it could mean anything you like.
 
 The script uses Dennis Ranke's solution from [The Ruby Quiz #2](www.rubyquiz.com/quiz2.html), which gives everyone a correct assignment in a single pass through the list. Nice! :) The only tweaks I made were practical ones, like using config files, and a tiny bit of refactoring, logging, etc, to make it more apparent what's happening.