Documentation: Python: Add notice about MSL compatibility

See #139185

doc/python_api/examples/gpu.1.py

@@ -84,6 +84,23 @@ Attributes are properties that are set using a vertex buffer and can be differen
 Uniforms are properties that are constant per draw call.
 They can be set using the ``shader.uniform_*`` functions after the shader has been bound.
 
+.. note::
+
+   It is important to note that GLSL sources are reinterpreted to MSL (Metal Shading Language) on Apple operating systems.
+   This uses a small compatibility layer that does not cover the whole GLSL language specification.
+   Here is a list of differences to keep in mind when targeting compatibility with Apple platforms:
+
+   * The only matrix constructors available are:
+
+      - diagonal scalar (example: ``mat2(1)``)
+      - all scalars (example: ``mat2(1, 0, 0, 1)``)
+      - column vector (example: ``mat2(vec2(1,0), vec2(0,1))``)
+      - reshape constructors work only for square matrices (example: ``mat3(mat4(1))``)
+
+   * ``vertex``, ``fragment`` and ``kernel`` are reserved keywords.
+   * all types and keywords defined by the `MSL specification <https://developer.apple.com/metal/Metal-Shading-Language-Specification.pdf>`__ are reserved keywords and should not be used.
+
+
 Batch Creation
 ++++++++++++++