[docs] Suggestion / Change Request - Add clarity to wait permission stacking

[NatPDeveloper]

File: docs/60_protocol-guides/40_accounts_and_permissions.md

Please add to the following

The potential actors who may execute the action are specified by either public key or account name in the authority table. Time waits are special factors which are satisfied by publishing a transaction with a delay in excess of the defined time. These carry weights as well that may contribute to satisfy the threshold.

Time waits may stack on one another. If for example a permission level has a threshold of 11 and 3 day wait which yield a weight of 2 and a 7 day wait with a weight of 4 and 11 accounts each with a weight of 1. Then after adding a delay of 1 week, 5 accounts would be required to pass the 11 threshold. (5 accounts at 1 weight each + 3 day wait at 2 weight + 7 day wait at 4 weight = 11).

Also note that the delay wait does not begin until the minimum threshold is met. So for the 3 day delay to start in the example above 9 signatures would be required. Upon the 9th signature signing, the delay begins and 3 days afterwards the transaction may be executed. Bear in mind this when assigning the expiration for a multi signature transaction.