docs: add GL_ARB_gl_spirv to features list

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
diff --git a/docs/features.txt b/docs/features.txt
index 9850a43..df81f91 100644
--- a/docs/features.txt
+++ b/docs/features.txt
@@ -282,6 +282,7 @@
   GL_ARB_compute_variable_group_size                    not started
   GL_ARB_ES3_2_compatibility                            DONE (i965/gen8+)
   GL_ARB_fragment_shader_interlock                      not started
+  GL_ARB_gl_spirv                                       not started
   GL_ARB_gpu_shader_int64                               started (airlied for core and Gallium, idr for i965)
   GL_ARB_indirect_parameters                            DONE (nvc0, radeonsi)
   GL_ARB_parallel_shader_compile                        not started, but Chia-I Wu did some related work in 2014