Asking a customer “how did you hear about us” on the cart page in Shopify

hear-about-us.liquid

{% assign choices = "Facebook, Twitter, Google, Best Toys Bulletin, John Doe" %}
{% assign required = true %}

<div class="form-vertical">
  <p>
    <label for="how-did-you-hear-about-us">How did you hear about us?</label>
    <select id="how-did-you-hear-about-us" name="attributes[how-did-you-hear-about-us]">
      <option value=""{% if cart.attributes.how-did-you-hear-about-us == "" %} selected{% endif %}>Please make a selection</option>
      {% assign optionsArray = choices | split: ',' %}
      {% for o in optionsArray %}
        {% assign option = o | strip %}
        <option value="{{ option }}"{% if cart.attributes.how-did-you-hear-about-us == option %} selected{% endif %}>{{ option }}</option>
      {% endfor %}
      <option value="Other"{% if cart.attributes.how-did-you-hear-about-us == "Other" %} selected{% endif %}>Other</option>
    </select>
  </p>
  <p style="{% unless cart.attributes.how-did-you-hear-about-us == 'Other' %}display:none;{% endunless %}">
    <label for="how-did-you-hear-about-us-other">Other:</label>
    <input id="how-did-you-hear-about-us-other" type="text" name="attributes[how-did-you-hear-about-us-other]" value="{{ cart.attributes.how-did-you-hear-about-us-other }}" />
  </p>
</div>

<script>
jQuery(function($) {
  $('#how-did-you-hear-about-us').change(function() {
    if ($('#how-did-you-hear-about-us').val() == 'Other') {
      $('#how-did-you-hear-about-us-other').parent('p').show();
    } else {
      $('#how-did-you-hear-about-us-other').val('').parent('p').hide();
    }
  });
  {% if required %}
  $('[name="checkout"], [name="goto_pp"], [name="goto_gc"]').click(function() {
    var validated = true;
    if ($('#how-did-you-hear-about-us').val() == '') {
      validated = false;    
    }
    else if ($('#how-did-you-hear-about-us').val() == 'Other') {
      if ($('#how-did-you-hear-about-us-other').val() == '') {
        validated = false; 
        $('#how-did-you-hear-about-us-other').addClass('error');
      } 
    }
    if(validated){
      $(this).submit();
    }
    else{
      alert("Please tell us how you heard about us.");
      return false;
    }
  });
  {% endif %}
});
</script>

Hi Caroline,
Just a question, if I want to add another option like "Other" with the possibility to write a comment for the client, for exemple: "how did you heard about us" and below of "Other" a new selection like: "on a blog" and the customer can write on which blog she saw us. Do you have instructions and code for that ?

PS : sorry for my englidh and thanks a lot for your help :))))