docs: list the new GLSL compiler

docs/relnotes-7.9.html

@@ -34,6 +34,9 @@ tbd
 
 <h2>New features</h2>
 <ul>
+<li>New, improved GLSL compiler written by Intel.
+    See the <a href="shading.html"> Shading Language</a> page for
+    more information.
 <li>GL_EXT_timer_query extension (i965 driver only)
 <li>GL_EXT_framebuffer_multisample extension (intel drivers, MAX_SAMPLES = 1)
 <li>GL_ARB_texture_swizzle extension (alias of GL_EXT_texture_swizzle)