docs: update Installation section

Author: aantipov

docs/getting-started/installation.md

@@ -13,3 +13,27 @@ yarn add vue-query
 ```
 
 Vue Query is compatible with Vue 2.x + composition API or 3.x
+
+### Vue Query Initialization
+
+Before starting using Vue Query, you need to initialize it.
+
+There are 2 possible ways to do it.
+
+1. [Vue 3 Only] Using `VueQueryPlugin` (recommended)
+
+```js
+import { VueQueryPlugin } from "vue-query";
+
+app.use(VueQueryPlugin);
+```
+
+1. Calling `useQueryProvider` in the root component
+
+```
+<script setup>
+import { useQueryProvider } from 'vue-query';
+
+useQueryProvider();
+</script>
+```