+Apart from the action names listed below, all actions starting with a '!' will
+be available as an external command. External commands can contain variable
+names that will be substituted before the command is run. Valid variable names
+are "%(head)", "%(commit)", and "%(blob)".
+
+As an example, the following external command will save the current commit as
+a patch file: "!git format-patch %(commit)^..%(commit)".
+