[PATCH] Add small comment about update option

[Wald Commits]

# HG changeset patch
# User Andre Heinecke <andre.heinecke at intevation.de>
# Date 1410963813 -7200
# Node ID e82c440c272786a574c14a9ccc581820a682bad0
# Parent  cf154e1f687a903de85748873e3814fe35adbf40
Add small comment about update option.

diff -r cf154e1f687a -r e82c440c2727 packaging/linux-installer.inc.in
--- a/packaging/linux-installer.inc.in	Wed Sep 17 15:06:03 2014 +0200
+++ b/packaging/linux-installer.inc.in	Wed Sep 17 16:23:33 2014 +0200
@@ -180,6 +180,8 @@
         shift 1
         ;;
       --update)
+# Update is an internal option that is used when the application calls
+# the installer to install an update.
         UPDATE=1
         shift 1
         ;;