Fix desktop categories

--- data/com.github.theironrobin.siglo.desktop.in
+++ data/com.github.theironrobin.siglo.desktop.in
@@ -3,7 +3,7 @@ Name=Siglo
 Exec=siglo
 Terminal=false
 Type=Application
-Categories=GTK;
+Categories=Utility;PDA;
 StartupNotify=true
 Icon=com.github.theironrobin.siglo
 X-Purism-FormFactor=Workstation;Mobile;