Document 'morphWithCount' and 'loadMorphCount' methods

eloquent-relationships.md

@@ -20,6 +20,7 @@
     - [Querying Relationship Absence](#querying-relationship-absence)
     - [Querying Polymorphic Relationships](#querying-polymorphic-relationships)
     - [Counting Related Models](#counting-related-models)
+    - [Counting Related Models On Polymorphic Relationships](#counting-related-models-on-polymorphic-relationships)
 - [Eager Loading](#eager-loading)
     - [Constraining Eager Loads](#constraining-eager-loads)
     - [Lazy Eager Loading](#lazy-eager-loading)
@@ -1075,6 +1076,34 @@ If you need to set additional query constraints on the eager loading query, you
         $query->where('rating', 5);
     }])
 
+<a name="counting-related-models-on-polymorphic-relationships"></a>
+### Counting Related Models On Polymorphic Relationships
+
+If you would like to eager load a `morphTo` relationship, as well as nested relationship counts on the various entities that may be returned by that relationship, you may use the `with` method in combination with the `morphTo` relationship's `morphWithCount` method.
+
+In this example, let's assume `Photo` and `Post` models may create `ActivityFeed` models. Additionally, let's assume that `Photo` models are associated with `Tag` models, and `Post` models are associated with `Comment` models.
+
+Using these model definitions and relationships, we may retrieve `ActivityFeed` model instances and eager load all `parentable` models and their respective nested relationship counts:
+
+    use Illuminate\Database\Eloquent\Relations\MorphTo;
+
+    $activities = ActivityFeed::query()
+        ->with(['parentable' => function (MorphTo $morphTo) {
+            $morphTo->morphWithCount([
+                Photo::class => ['tags'],
+                Post::class => ['comments'],
+            ]);
+        }])->get();
+
+In addition, you may use the `loadMorphCount` method to eager load all nested relationship counts on the various entities of the polymorphic relation if the `ActivityFeed` models have already been retrieved:
+
+    $activities = ActivityFeed::with('parentable')
+        ->get()
+        ->loadMorphCount('parentable', [
+            Photo::class => ['tags'],
+            Post::class => ['comments'],
+        ]);
+
 <a name="eager-loading"></a>
 ## Eager Loading