Also add a one-line description of the "optional" directive.
diff --git a/Mac/Tools/macfreeze/directives.py b/Mac/Tools/macfreeze/directives.py
index 16b7879..3ef9661 100644
--- a/Mac/Tools/macfreeze/directives.py
+++ b/Mac/Tools/macfreeze/directives.py
@@ -8,6 +8,7 @@
# The directives supported are
# include - Include a module or file
# exclude - Exclude a module
+# optional - Include a module if it is found, but don't complain if it isn't
# path - Add sys.path entries. Relative paths are relative to the source file.
#
# See the macfreeze.py main program for a real live example.