docs/features: Add GL_EXT_multisampled_render_to_texture

Currently only a6xx, panfrost added later in series.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Acked-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6161>
diff --git a/docs/features.txt b/docs/features.txt
index 63b7d8c..ed82a09 100644
--- a/docs/features.txt
+++ b/docs/features.txt
@@ -321,6 +321,7 @@
   GL_EXT_memory_object                                  DONE (radeonsi)
   GL_EXT_memory_object_fd                               DONE (radeonsi)
   GL_EXT_memory_object_win32                            not started
+  GL_EXT_multisampled_render_to_texture                 DONE (freedreno/a6xx)
   GL_EXT_render_snorm                                   DONE (i965, r600, radeonsi)
   GL_EXT_semaphore                                      DONE (radeonsi)
   GL_EXT_semaphore_fd                                   DONE (radeonsi)