Update Best Practices and FAQ.md

Guides/Best Practices and FAQ.md

@@ -10,12 +10,21 @@ If this assert is ever hit, that means `IGListKit` has sent your section control
 This would only happen if your objects provide *non-unique* diff identifiers. 
 
 ```objective-c
+// Objective-C
 - (void)didUpdateToObject:(id)object {
     NSParameterAssert([object isKindOfClass:[MyModelClass class]]);
     _myModel = object;
 }
 ```
 
+```swift
+// Swift
+func didUpdate(to object: Any) {
+    precondition(object is MyModelClass)
+    myModel = object as! MyModelClass
+}
+```
+
 - Make sure your [`-diffIdentifier`](https://instagram.github.io/IGListKit/Protocols/IGListDiffable.html#/c:objc(pl)IGListDiffable(im)diffIdentifier) implementation returns a **unique identifier** for each object.
 
 - We highly recommend using single-item sections when possible. That is, each section controller manages a single model (which may have one or multiple cells). This gives you the greatest amount of flexibility, modularity, and re-use for your components.