Add followers when click button save on po

Nyuper function create

@api.model
    def create(self, vals):
        res = super(PurchaseOrder, self).create(vals)
        group_id = self.env.ref('branch_purchase.branch_confirm_rfq').id
        branch_confirm_rfq_users = self.env['res.users'].
            search([('branch_id', '=', self.env.user.partner_id.branch_id.id),
    ('groups_id', 'in', [group_id])]).ids
        res.message_subscribe_users(branch_confirm_rfq_users)
        return res