Custom contents below voucher field in shopping cart

I do not know how to create a new hook, I would like to insert text here (in yellow) in ma cart page

Display custom contents from html box pro below voucher field in shopping cart

This position is located in file themes/your-thjeme/shopping-cart.tpl

if you will put your hook execution code right below code:

{if $voucherAllowed}

            <form action="{if $opc}{$link->getPageLink('order-opc', true)}{else}{$link->getPageLink('order', true)}{/if}" method="post" id="voucher">

          <fieldset>

              <h4>{l s='Vouchers'}</h4>

              <input type="text" class="discount_name form-control" id="discount_name" name="discount_name" value="{if isset($discount_name) && $discount_name}{$discount_name}{/if}" />

              <input type="hidden" name="submitDiscount" />

              <button type="submit" name="submitAddDiscount" class="button btn btn-default button-small"><span>{l s='OK'}</span></button>

          </fieldset>

            </form>

            {if $displayVouchers}

          <p id="title" class="title-offers">{l s='Take advantage of our exclusive offers:'}</p>

          <div id="display_cart_vouchers">

              {foreach $displayVouchers as $voucher}

            {if $voucher.code != ''}<span class="voucher_name" data-code="{$voucher.code|escape:'html':'UTF-8'}">{$voucher.code|escape:'html':'UTF-8'}</span> - {/if}{$voucher.name}<br />

              {/foreach}

          </div>

            {/if}

{/if}

your contents will appear right below the input field - exactly there where you show on your screenshot :)