Update loop unroll docs

docs/api/en/materials/ShaderMaterial.html

@@ -54,6 +54,12 @@
 					<li>
 						The loop variable has to be *i*.
 					</li>
+					<li>
+						Array accesses within the loop must include spaces around the index: <b>array[ i ]</b>.
+					</li>
+					<li>
+						The value *UNROLL_LOOP_INDEX* will be replaced with the explicity value of *i* for the given iteration and can be used in preprocessor statements.
+					</li>
 				</ul>
 				<code>
 		#pragma unroll_loop_start