gif should be handled by mpv in mailcap

rtv/templates/mailcap

@@ -26,6 +26,7 @@
 # Note that rtv returns a list of urls for imgur albums, so we don't put quotes
 # around the `%s`
 image/x-imgur-album; feh -g 640x480 %s; test=test -n "$DISPLAY"
+image/gif; mpv '%s' --autofit 640x480 --loop=inf; test=test -n "$DISPLAY"
 image/*; feh -g 640x480 '%s'; test=test -n "$DISPLAY"
 
 # Youtube videos are assigned a custom mime-type, which can be streamed with