[gnome-boxes] help: Add missing page to Makefile

[Piotr Drąg <piotrdrag src gnome org>]

commit 9de843aec1b160a53b7716d0628df7774c8c0ad7
Author: Piotr Drąg <piotrdrag gmail com>
Date:   Sun Feb 4 21:41:26 2018 +0100

    help: Add missing page to Makefile

 help/Makefile.am | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/help/Makefile.am b/help/Makefile.am
index ac9a72c4..6ab9f460 100644
--- a/help/Makefile.am
+++ b/help/Makefile.am
@@ -19,6 +19,7 @@ HELP_FILES = index.page                       \
        prop-system.page                \
        prop-trouble.page               \
        search.page                     \
+       shared-folders.page             \
        shortcuts.page                  \
        shutdown.page                   \
        snapshot-create.page            \