[ruby/timeout] [DOC] document the private instance method

ruby/timeout@52e85fed75

Author: nobu

lib/timeout.rb

@@ -305,6 +305,7 @@ def self.timeout(sec, klass = nil, message = nil, &block)   #:yield: +sec+
     end
   end
 
+  # See Timeout.timeout
   private def timeout(*args, &block)
     Timeout.timeout(*args, &block)
   end