DOCS: document --input-preprocess-wheel option

Document the use cases for enabling or disabling the wheel preprocessing.
Also note that this option has no effect on any filtering already done
by the OS/driver.

DOCS/interface-changes.rst

@@ -30,6 +30,7 @@ Interface changes
     - add `--volume-gain`, `--volume-gain-min`, and `--volume-gain-max` options
     - add `current-gpu-context` property
     - add `--secondary-sub-ass-override` option
+    - add `--input-preprocess-wheel` option
     - remove shared-script-properties (user-data is a replacement)
     - add `--secondary-sub-delay`, decouple secondary subtitles from
       `--sub-delay`

DOCS/man/options.rst

@@ -4195,6 +4195,20 @@ Input
     implemented. Whether media keys work when the mpv window is focused is
     implementation-defined.
 
+``--input-preprocess-wheel=<yes|no>``
+    Preprocess ``WHEEL_*`` events so that while scrolling on the horizontal
+    or vertical direction, the events aren't generated for another direction
+    even when the two directions are scrolled together (default: yes).
+
+    This preprocessing can be beneficial for preventing accidentally seeking
+    while changing the volume by scrolling on a touchpad with the default
+    keybind. Due to the deadzone mechanism used, disabling the preprocessing
+    allows for diagonal scrolling (such as panning) and potentially reduces
+    input latency.
+
+    Note that disabling the preprocessing does not affect any filtering done
+    by the OS/driver before these events are delivered to mpv, if any.
+
 ``--input-right-alt-gr``, ``--no-input-right-alt-gr``
     (macOS and Windows only)
     Use the right Alt key as Alt Gr to produce special characters. If disabled,