Documenting ASWeakProxy (#2328)

AsyncDisplayKit/Details/ASWeakProxy.h

@@ -14,8 +14,20 @@
 
 @interface ASWeakProxy : NSProxy
 
+/**
+ * @return target The target which will be forwarded all messages sent to the weak proxy.
+ */
 @property (nonatomic, weak, readonly) id target;
 
+/**
+ * An object which forwards messages to a target which it weakly references
+ *
+ * @discussion This class is useful for breaking retain cycles. You can pass this in place
+ * of the target to something which creates a strong reference. All messages sent to the
+ * proxy will be passed onto the target.
+ *
+ * @return an instance of ASWeakProxy
+ */
 + (instancetype)weakProxyWithTarget:(id)target;
 
 @end