DOCS/man/options: add some description for sdr-adjust-gamma

Add some description about output metadata.

Signed-off-by: Shengyu Qu <[email protected]>

Author: Headcrabed

DOCS/man/options.rst

@@ -7380,7 +7380,10 @@ them.
     explicitly set, in which case it behaves like ``yes``.
 
     Generally it's recommended to enable this option, if you can ensure that
-    both source and target metadata is correct.
+    both source and target metadata is correct. If you are using macOS, Windows
+    with ACM enabled, or Wayland that compositor has color management protocol
+    support, and ``--gpu-api`` set to ``d3d11`` or ``vulkan``(``opengl`` won't
+    work), output metadata should be always correct.
 
     (Only for ``--vo=gpu-next``)