gallium-docs: Add note on scissor.
diff --git a/src/gallium/docs/source/context.rst b/src/gallium/docs/source/context.rst
index b7b625d..78b01cc 100644
--- a/src/gallium/docs/source/context.rst
+++ b/src/gallium/docs/source/context.rst
@@ -54,7 +54,10 @@
* ``set_blend_color``
* ``set_clip_state``
* ``set_polygon_stipple``
-* ``set_scissor_state``
+* ``set_scissor_state`` sets the bounds for the scissor test, which culls
+ pixels before blending to render targets. If the :ref:`Rasterizer` does
+ not have the scissor test enabled, then the scissor bounds never need to
+ be set since they will not be used.
* ``set_viewport_state``
* ``set_vertex_elements``