Enhancement - en passant "done"

- When marking task(s) as done, it is now possible to modify them
  at the same time.

src/task.cpp

@@ -220,6 +220,10 @@ static std::string shortUsage (Config& conf)
       << "full tutorial.  New releases containing fixes and enhancements are "
       << "made frequently."
       << std::endl
+      << std::endl
+      << "Join in the discussion of task, present and future, at "
+      << "http://groups.google.com/group/taskprogram"
+      << std::endl
       << std::endl;
 
   return out.str ();