docs: add deprecation warning to wapper contains (vuejs#1612)

Author: SmilingJoe

docs/api/wrapper/contains.md

@@ -1,5 +1,9 @@
 ## contains
 
+::: warning Deprecation warning
+Using `contains` is deprecated and will be removed in future releases. Use [`find`](./find.md) for DOM nodes (using `querySelector` syntax), [`findComponent`](./findComponent.md) for components, or [`wrapper.get`](./get.md) instead.
+:::
+
 Assert `Wrapper` contains an element or component matching [selector](../selectors.md).
 
 - **Arguments:**