docs: Mention PIPE_CAP_TEXTURE_BUFFER_SAMPLER

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <!8300>

docs/gallium/context.rst

@@ -124,9 +124,10 @@ objects. They all follow simple, one-method binding calls, e.g.
 Samplers
 ^^^^^^^^
 
-pipe_sampler_state objects control how textures are sampled (coordinate
-wrap modes, interpolation modes, etc).  Note that samplers are not used
-for texture buffer objects.  That is, pipe_context::bind_sampler_views()
+pipe_sampler_state objects control how textures are sampled
+(coordinate wrap modes, interpolation modes, etc).  Note that unless
+``PIPE_CAP_TEXTURE_BUFFER_SAMPLER`` is enabled, samplers are not used for
+texture buffer objects.  That is, pipe_context::bind_sampler_views()
 will not bind a sampler if the corresponding sampler view refers to a
 PIPE_BUFFER resource.