Add usage info for the --force option

hg-fast-export.sh

@@ -29,6 +29,8 @@ Options:
 	-r	Mercurial repository to import
 	-M	Set the default branch name (default to 'master')
 	-o	Use <name> as branch namespace to track upstream (eg 'origin')
+	--force Ignore validation errors when converting, and pass --force
+		to git-fast-import(1)
 "
 
 . "$(git --exec-path)/git-sh-setup"