message: [lang/tests] Add doc comment to state struct of Erc20 example
diff: @@ -24,6 +24,7 @@ use pdsl_core::{
  use pdsl_lang::contract;
  contract! {
  + /// The storage items for a typical ERC20 token implementation.
  struct Erc20 {
  /// All peeps done by all users.
  balances: storage::HashMap<Address, Balance>,
  