Re-add Place to write client PO number

[Ahmad-A2Z-Orders]

@lubos
Dear, Lubos

is it possible to re-put the order number again as before
it was beneficial to put each purchase order number coming from clients in the invoice ( this is an important term from clients to put the PO number on each invoice)
now I put it manually in the description and update it with every new delivery note I made it

Check the attached photos please

[Tut]

You can do this with a custom field.