docs: add link to the GLSL compiler page

This reverts commit 9e0931e355a21ff9902a4127cc63b392d8def0cd

Reviewed-by: Brian Paul <brianp@vmware.com>
diff --git a/docs/contents.html b/docs/contents.html
index b9a8922..5752299 100644
--- a/docs/contents.html
+++ b/docs/contents.html
@@ -58,6 +58,7 @@
 
 <b>User Topics</b>
 <ul>
+<li><a href="shading.html" target="_parent">Shading Language</a>
 <li><a href="egl.html" target="_parent">EGL</a>
 <li><a href="opengles.html" target="_parent">OpenGL ES</a>
 <li><a href="openvg.html" target="_parent">OpenVG / Vega</a>