docs: document improved stencil support and GL_EXT_vertex_array_bgra

docs/relnotes-7.5.html

@@ -33,6 +33,10 @@ tbd
 <h2>New features</h2>
 <ul>
 <li>GL_ARB_framebuffer_object extension (software drivers, i965 driver)
+<li>Reworked two-sided stencil support.
+This allows a driver to support all three variations of two-sided stencil
+including GL_ATI_separate_stencil, GL_EXT_stencil_two_side and OpenGL 2.0
+<li>GL_EXT_vertex_array_bgra extension (software drivers, i965 driver)
 </ul>