Small mpv updates

- Add some comments for the heck of it
- Add playlist seek hotkeys
- Add keyboard volume controls

.config/mpv/input.conf

@@ -1,6 +1,8 @@
-# Mouse wheel volume
+# Mouse wheel and +/- volume
 WHEEL_UP      add volume 5
 WHEEL_DOWN    add volume -5
+=             add volume 5
+-             add volume -5
 
 # Arrow keys seek
 RIGHT seek  5
@@ -13,6 +15,10 @@ Q quit
 F cycle fullscreen
 S screenshot
 
+# I almost never open multiple files but when I do, I want seek controls
+> playlist-next
+< playlist-prev
+
 # If I leave a video on and go to bed, this dims the video feed significantly
 n set brightness -40;set gamma -40;show-text "Night Mode On"
 N set brightness 0;set gamma 0;show-text "Night Mode Off"