docs: remove generic type from state selection

The generic type is not necessary and causes error in compilation because it expects the state key instead of the state key type.

docs/store/README.md

@@ -96,7 +96,7 @@ export class MyAppComponent {
 	counter: Observable<number>;
 
 	constructor(private store: Store<AppState>) {
-		this.counter = store.select<number>((state: AppState) => state.counter);
+		this.counter = store.select('counter');
 	}
 
 	increment(){