Drop implementation details from instructions.append.md

The implementation details should be understandable from the stubs and
tests.

Author: IsaacG

exercises/practice/bank-account/.docs/instructions.append.md

@@ -1,36 +1,5 @@
 # Instructions append
 
-## Implementation Notes
-
-### Opening an account
-
-An account can be opened.
-On opening, its initial balance should not be negative.
-If a negative balance is given to the `Open` function, `nil` must be returned, otherwise the newly created account must be returned.
-
-### Closing an account
-
-An account can be closed.
-When closing an account, the `Close` method must return the balance the account has and a boolean `true` indicating the account was closed successfully.
-Closing an account does not succeed if the account is already closed.
-When an account is closed, its balance must be set to `0`.
-
-### Getting the account balance
-
-The `Balance` method allows a user to check the current balance of an account.
-It must return the balance of the account and a boolean indicating if the operation succeeded.
-Checking the balance only doesn't succeed if the account is closed.
-
-### Deposits / Withrawals
-
-Deposits and withdrawals are both handled by the `Deposit` method.
-If the argument given to the method is a positive amount, then that amount of money must be deposited in the account.
-If the amount given is negative, that amount of money must be withdrawn from the account.
-If the account is closed, its balance must not be modified.
-
-`Deposit` returns the new balance of the account and a boolean that indicates if the operation succeeded.
-`Deposit` must fail if the account is closed or if there is not enough money to withdraw from the account.
-
 ## Testing
 
 The tests will execute some operations concurrently.