Update multi-signatures.md

[GordonLtron]

This is an update for Procedure for Modifying Permissions

1. Permission Modification Operation Process

1. Check Current Account Permissions
   Use the getaccount command to query and review the current permission structure of the SR account.
2. Prepare the New Witness Account.
3. Stop the Current SR Node.
   4.Update Witness Permission via Smart Contract.
   Using the SR's owner account, initiate the AccountPermissionUpdateContract transaction (cost: 100 TRX).
4. Modify SR Node Configuration, update the local config file of your SR node.Replace the existing private key with the private key of the new witness account.
5. Restart the SR Node.

Warning!
You must stop the currently producing SR node before broadcasting the AccountPermissionUpdateContract transaction.

An SR node cannot package a transaction that modifies its own witness permission into a block. If a node attempts to produce a block containing such a transaction, the block will fail signature verification. As a penalty, the node will be disconnected from the network by other peers for 1 hour.