docs: mention the new Gallium llvmpipe driver

docs/relnotes-7.6.html

@@ -57,6 +57,10 @@ This was written by Zack Rusin at Tungsten Graphics.
     GL_ARB_fragment_program.</li>
 <li>Added configure --with-max-width=W, --with-max-height=H options to specify
     max framebuffer, viewport size.
+<li>Initial version of Gallium llvmpipe driver.  This is a new driver based
+    on LLVM which makes exensive use of run-time code generation.  This is
+    an "alpha" stage driver.  See the src/gallium/drivers/llvmpipe/README
+    file for more information.
 </ul>