docs(vue): update docs for instantiated store

Author: blimmer

docs/vue-testing-library/api.mdx

@@ -69,7 +69,7 @@ Additionally, the following options can also be provided:
 
 The object definition of a [Vuex](https://vuex.vuejs.org/) store. If a `store`
 object is provided, `Vue Testing Library` will import and configure a Vuex
-store.
+store. If an instantiated Vuex store is passed, it will be used.
 
 ##### `routes` (`Array`)