[gnome-documents] Add a missing tag to the AppData file

[Richard Hughes <rhughes src gnome org>]

commit 209af2c5db42fde240a7114cb6b8992b62e0f50a
Author: Richard Hughes <richard hughsie com>
Date:   Mon Jan 25 13:06:55 2016 +0000

    Add a missing tag to the AppData file

 data/org.gnome.Documents.appdata.xml.in |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/data/org.gnome.Documents.appdata.xml.in b/data/org.gnome.Documents.appdata.xml.in
index 4139ed6..a0b6c00 100644
--- a/data/org.gnome.Documents.appdata.xml.in
+++ b/data/org.gnome.Documents.appdata.xml.in
@@ -45,4 +45,5 @@
       <image 
type="source">https://git.gnome.org/browse/gnome-documents/plain/data/screenshots/gnome-documents-3.png</image>
     </screenshot>
   </screenshots>
+  <project_group>GNOME</project_group>
 </application>