[DOC] store: clarify how a component can find a store

closes #617

doc/reference/store.md

@@ -208,7 +208,11 @@ Note that getters are not cached.
 ### Connecting a Component
 
 At some point, we need a way to interact with the store from a component. This
-can be done with the help of the three store hooks:
+means that the component needs a reference to the store. By default, it looks
+for it in the `env.store` key. However, this can be configured with the `useStore`
+hook.
+
+Every component-store interactions are done with the help of the three store hooks:
 
 - [`useStore`](#usestore) to subscribe a component to some part of the store state,
 - [`useDispatch`](#usedispatch) to get a reference to a dispatch function,
@@ -229,6 +233,14 @@ const state = {
 const store = new owl.Store({ state, actions });
 ```
 
+To make it accessible to the complete application, we will put it in the
+environment:
+
+```js
+// in this example, the root component is App
+App.env.store = store;
+```
+
 A counter component can then select this value and dispatch an action like this:
 
 ```js