Improve RS documentation.

bug 8570568
Change-Id: I465fcc8ec3e2cc892dc3cb0067aacf5224338102
diff --git a/graphics/java/android/renderscript/ScriptC.java b/graphics/java/android/renderscript/ScriptC.java
index 6975534..b0a5759 100644
--- a/graphics/java/android/renderscript/ScriptC.java
+++ b/graphics/java/android/renderscript/ScriptC.java
@@ -30,7 +30,8 @@
 import java.lang.reflect.Modifier;
 
 /**
- *
+ * The superclass for all user-defined scripts. This is only
+ * intended to be used by the generated derived classes.
  **/
 public class ScriptC extends Script {
     private static final String TAG = "ScriptC";