chore: add example for balance AccountStore (#10361)

* chore: modified example for balance AccountStore

* add example for account store balance

* add example for account store balance

* Update frame/balances/src/lib.rs

* Update frame/balances/src/lib.rs

* balance account store example

* balance account store example

* Update frame/balances/src/lib.rs

* Update frame/balances/src/lib.rs

* balance account store example

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>
Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>