docs: Update for EGL environment variables.

Mention that EGL_DRIVER should be a full path, and add a link from
envvars.html to egl.html.

docs/egl.html

@@ -128,8 +128,9 @@ runtime</p>
 <ul>
 <li><code>EGL_DRIVER</code>
 
-<p>This variable forces the specified EGL driver to be loaded.  It comes in
-handy when one wants to test a specific driver.</p>
+<p>This variable specifies a full path to an EGL driver and it forces the
+specified EGL driver to be loaded.  It comes in handy when one wants to test a
+specific driver.</p>
 
 </li>
 

docs/envvars.html

@@ -69,6 +69,10 @@ These environment variables are for the Radeon R300 driver:
 <li>R300_NO_TCL - if set, disable hardware-accelerated Transform/Clip/Lighting.
 </ul>
 
+<p>
+Mesa EGL supports different sets of environment variables.  See the
+<a href="egl.html">Mesa EGL</a> page for the details.
+</p>
 
 </BODY>
 </HTML>