Merge branch 'add-categories' into 'master'

Add standard categories to desktop file

See merge request postmarketOS/megapixels!6

data/org.postmarketos.Megapixels.desktop

@@ -3,7 +3,7 @@ Name=Megapixels
 Exec=megapixels
 Terminal=false
 Type=Application
-Categories=GTK;
+Categories=GTK;Photography;Graphics;
 Icon=org.postmarketos.Megapixels
 X-Purism-FormFactor=Workstation;Mobile;
 StartupNotify=true