title: How do I add checkboxes to admin-on-rest admin on rest create form and post the checkbox value to backend
body: <p>I have added the material-ui/Checkbox component in admin-on-rest create form with <strong>source</strong> attribute. But after I click save button, I could not see the checkbox value in posted data.</p>
  
  <p>But I can see 'title' and 'body' fields value in posted data. Can someone please tell, Why this code is not working?</p>
  
  <p>Here is my sample code:</p>
  
  <pre><code>export const PostCreate = (props) =&gt; (
          &lt;Create {...props} &gt;
              &lt;SimpleForm&gt;
                  &lt;TextInput source="title" /&gt;
                  &lt;LongTextInput source="body" /&gt;
                  &lt;Checkbox
                      label="Label on the left"
                      labelPosition="left"
                      source="test"
                      value="yes"
                  /&gt;
      &lt;/SimpleForm&gt;&lt;/Create&gt;
      );
  </code></pre>