Examples: Add GPGPU bird to examples index list

examples/index.html

@@ -143,6 +143,7 @@
 				"webgl_geometry_terrain_raycast",
 				"webgl_geometry_tessellation",
 				"webgl_geometry_text",
+				"webgl_gpgpu_birds",
 				"webgl_hdr",
 				"webgl_helpers",
 				"webgl_interactive_cubes",