docs: document MESA_GLES_VERSION_OVERRIDE envvar

v2: Removed reference to FC not being an allowed suffix (Brian Paul)

Reviewed-by: Brian Paul <brianp@vmware.com>
diff --git a/docs/envvars.html b/docs/envvars.html
index ba83335..8c4597c 100644
--- a/docs/envvars.html
+++ b/docs/envvars.html
@@ -91,6 +91,14 @@
 <li> Mesa may not really implement all the features of the given version.
 (for developers only)
 </ul>
+<li>MESA_GLES_VERSION_OVERRIDE - changes the value returned by
+glGetString(GL_VERSION) for OpenGL ES.
+<ul>
+<li> The format should be MAJOR.MINOR
+<li> Examples: 2.0, 3.0, 3.1
+<li> Mesa may not really implement all the features of the given version.
+(for developers only)
+</ul>
 <li>MESA_GLSL_VERSION_OVERRIDE - changes the value returned by
 glGetString(GL_SHADING_LANGUAGE_VERSION). Valid values are integers, such as
 "130".  Mesa will not really implement all the features of the given language version