Update materials_overview.adoc

Second pass at making table 1 more readable by setting column widths to 20,40.40.

src/docs/asciidoc/jme3/advanced/materials_overview.adoc

@@ -46,8 +46,9 @@ jMonkeyEngine supports illuminated and unshaded Material Definitions.
 *  Phong Illuminated materials look more naturalistic.
 *  Unshaded materials look more abstract. 
 
-“Unshaded materials look somewhat abstract because they ignore lighting and shading. Unshaded Materials work even if the scene does not include a light source. These Materials can be single-colored or textured. For example, they are used for cards and tiles, for the sky, billboards and UI elements, for toon-style games, or for testing. 
-[cols="3", options="header", caption=]
+“Unshaded materials look somewhat abstract because they ignore lighting and shading. Unshaded Materials work even if the scene does not include a light source. These Materials can be single-colored or textured. For example, they are used for cards and tiles, for the sky, billboards and UI elements, for toon-style games, or for testing.
+
+[cols="20,40,40", options="header", caption=]
 .Material Definition
 |===