Improve layout spec block documentation (#2547)

Author: maicki

AsyncDisplayKit/ASDisplayNode+Subclasses.h

@@ -160,7 +160,7 @@ NS_ASSUME_NONNULL_BEGIN
  * be done before display can be performed here, and using ivars to cache any valuable intermediate results is
  * encouraged.
  *
- * @note This method should not be called directly outside of ASDisplayNode; use -measure: or -calculatedLayout instead.
+ * @note This method should not be called directly outside of ASDisplayNode; use -layoutThatFits: instead.
  *
  * @warning Subclasses that implement -layoutSpecThatFits: must not use .layoutSpecBlock. Doing so will trigger an
  * exception. A future version of the framework may support using both, calling them serially, with the .layoutSpecBlock

AsyncDisplayKit/ASDisplayNode.h

@@ -280,6 +280,8 @@ extern NSInteger const ASDefaultDrawingPriority;
  * @warning Subclasses that implement -layoutSpecThatFits: must not also use .layoutSpecBlock. Doing so will trigger
  * an exception. A future version of the framework may support using both, calling them serially, with the
  * .layoutSpecBlock superseding any values set by the method override.
+ *
+ * @code ^ASLayoutSpec *(__kindof ASDisplayNode * _Nonnull node, ASSizeRange constrainedSize) {};
  */
 @property (nonatomic, readwrite, copy, nullable) ASLayoutSpecBlock layoutSpecBlock;