add blank material files

cstrike/pbr/models/grass.mdl/grass.mdl.mat

@@ -0,0 +1,8 @@
+
+{
+"for" "#models/grass/grassblades.mdl"
+//"basecolor_map" "grassblades.png"
+//"normal_map" "grassblades_normal.png"
+//"metal_map" "grassblades_metal.png"
+//"roughness_map" "grassblades_roughness.png"
+}