[api] Add documentation for PropertyAttribute enum.

include/v8.h

Index: include/v8.h
diff --git a/include/v8.h b/include/v8.h
index fa572b0a00e2d9f1517ef5fd4448c547453657c3..8fc9149671a9795d3a797e543d8f8ae4f29c3ba6 100644
--- a/include/v8.h
+++ b/include/v8.h
@@ -2673,11 +2673,17 @@ class V8_EXPORT Uint32 : public Integer {
   static void CheckCast(v8::Value* obj);
 };
 
-
+/**
+ * PropertyAttribute.
+ */
 enum PropertyAttribute {
-  None       = 0,
-  ReadOnly   = 1 << 0,
-  DontEnum   = 1 << 1,
+  /** None. **/
+  None = 0,
+  /** ReadOnly, i.e., not writable. **/
+  ReadOnly = 1 << 0,
+  /** DontEnum, i.e., not enumerable. **/
+  DontEnum = 1 << 1,
+  /** DontDelete, i.e., not configurable. **/
   DontDelete = 1 << 2
 };