document :boolean option flag

lib/yawpa.rb

@@ -32,6 +32,7 @@ module Yawpa
   #     server: {nargs: (1..2)},
   #     username: {nargs: 1},
   #     password: {nargs: 1},
+  #     color: {boolean: true},
   #   }
   #
   # The keys of the +options+ Hash can be either strings or symbols.
@@ -42,6 +43,8 @@ module Yawpa
   # - +:short+: specify a short option letter to associate with the long option
   # - +:nargs+: specify an exact number or range of possible numbers of
   #   arguments to the option
+  # - +:boolean+: if true, specify that the option is a toggleable boolean
+  #   option and allow a prefix of "no" to turn it off.
   #
   # @param params [Array]
   #   List of program parameters to parse.