title: How to create a metafield on Shopify using API?
body: <p>I want to create a meta field for a customer on a Shopify site when he is logged in, 
  I have gone through all forums and the docs of Shopify but no success.</p>
  
  <p>I found this link (<a href="http://www.shopify.com/technology/3032322-new-feature-metafields" rel="nofollow">http://www.shopify.com/technology/3032322-new-feature-metafields</a>) where it can be done through API but I don't know how to use this on liquid theme. The following is an example provided on above URL:</p>
  
  <pre><code>&lt;code&gt;
  product = ShopifyAPI::Product.find(product_id)
  product.add_metafield(ShopifyAPI::Metafield.new({
     :description =&gt; 'Author of book',
     :namespace =&gt; 'book',
     :key =&gt; 'author',
     :value =&gt; 'Kurt Vonnegut',
     :value_type =&gt; 'string'
  }))
  &lt;/code&gt;
  </code></pre>
  
  <p>Please guide me on this so I can finish it.</p>