docs: update ARB_buffer_storage status

Reviewed-by: Fredrik Höglund <fredrik@kde.org>
diff --git a/docs/GL3.txt b/docs/GL3.txt
index 542ee28..54a0c51 100644
--- a/docs/GL3.txt
+++ b/docs/GL3.txt
@@ -170,7 +170,7 @@
 
   GLSL 4.4                                             not started
   GL_MAX_VERTEX_ATTRIB_STRIDE                          not started
-  GL_ARB_buffer_storage                                not started
+  GL_ARB_buffer_storage                                DONE (r300, r600, radeonsi)
   GL_ARB_clear_texture                                 not started
   GL_ARB_enhanced_layouts                              not started
   GL_ARB_multi_bind                                    started (Fredrik Höglund)