DOCS/man: note that default autoprobe order is unrealiable

The default values for --ao, --vo, --gpu-api, --gpu-context change from
time to time, but some libmpv clients rely on the existing autoprobe order
and breaks as a result when the value changes. This specifies that the
default autoprobe order should not be relied upon.

DOCS/man/ao.rst

@@ -15,6 +15,10 @@ in the list.
     See ``--ao=help`` for a list of compiled-in audio output drivers sorted by
     autoprobe order.
 
+    Note that the default audio output driver is subject to change, and must
+    not be relied upon. If a certain AO needs to be used, it must be
+    explicitly specified.
+
 Available audio output drivers are:
 
 ``alsa``

DOCS/man/options.rst

@@ -6447,6 +6447,9 @@ them.
     order. You can also pass ``help`` to get a complete list of compiled in backends
     (sorted by the default autoprobe order).
 
+    Note that the default GPU context is subject to change, and must not be relied upon.
+    If a certain GPU context needs to be used, it must be explicitly specified.
+
     auto
         auto-select (default). Note that this context must be used alone and
         does not participate in the priority list.
@@ -6489,7 +6492,9 @@ them.
     Controls which type of graphics APIs will be accepted:
 
     auto
-        Use any available API (default)
+        Use any available API (default). Note that the default GPU API used for this
+        value is subject to change, and must not be relied upon. If a certain GPU API
+        needs to be used, it must be explicitly specified.
     opengl
         Allow only OpenGL (requires OpenGL 2.1+ or GLES 2.0+)
     vulkan

DOCS/man/vo.rst

@@ -19,6 +19,10 @@ in the list.
     does not work, it will fallback to other drivers (in the same order as
     listed by ``--vo=help``).
 
+    Note that the default video output driver is subject to change, and must
+    not be relied upon. If a certain VO needs to be used (e.g. for ``libmpv``
+    rendering API), it must be explicitly specified.
+
 Available video output drivers are:
 
 ``gpu``