Update tools.rst

Update tools.rst
- line 541 : the notification code is 'ACQ_NOTIF_ON_RECEIV' and not 'ACQ_NOTIF_ON_REVEIV'
- line 546 : the notification code is 'AR\_CANCELED' and not 'AR\_CANCELLED'
- line 1245 : the example in the manual lets me think we're talking about patrons and not items, that's why I propose to write 'Add patron('s)' instead of 'Add item(s)'