docs: document gl_TextureMatrix[i][j] array indexing bug fix

docs/relnotes-7.5.html

@@ -71,6 +71,7 @@ including GL_ATI_separate_stencil, GL_EXT_stencil_two_side and OpenGL 2.0
 <li>Increased max number of generic GLSL varying variables to 16 (formerly 8).
 <li>GLSL linker now detects when too many varying variables are used.
 <li>Optimize-out redundant glMaterial and glShadeModel calls in display lists
+<li>Fixed gl_TextureMatrix[i][j] array indexing bug in GLSL compiler.
 </ul>