input.conf: bind MBTN_MID to align-to-cursor

DOCS/man/mpv.rst

@@ -383,6 +383,9 @@ Left double click
 Right click
     Toggle pause on/off.
 
+Middle click
+    Pan through the whole video while holding the button.
+
 Forward/Back button
     Skip to next/previous entry in playlist.
 

etc/input.conf

@@ -31,6 +31,7 @@
 #MBTN_LEFT     ignore              # don't do anything
 #MBTN_LEFT_DBL cycle fullscreen    # toggle fullscreen
 #MBTN_RIGHT    cycle pause         # toggle pause/playback mode
+#MBTN_MID      script-binding positioning/align-to-cursor # pan the whole video
 #MBTN_BACK     playlist-prev       # skip to the previous file
 #MBTN_FORWARD  playlist-next       # skip to the next file
 #Ctrl+MBTN_LEFT script-binding positioning/drag-to-pan # pan around the clicked point