title: how to add new field in configuration in magento (extend from core)
body: <p>Hye, I would like to ask, how to <strong>add a new field in configuration</strong> extend from core. example i want to put a new field call test in system->configuration->general->store information.</p>
  
  <p>I know is wrong, but this is the file that i use:-</p>
  
  <p>MageCustom/GST/etc/system.xml</p>
  
  <pre><code>&lt;config&gt;
  &lt;tabs&gt;
      &lt;customer translate="label" module="customer"&gt;
          &lt;label&gt;dd&lt;/label&gt;
          &lt;sort_order&gt;300&lt;/sort_order&gt;
      &lt;/customer&gt;
  &lt;/tabs&gt;
  &lt;sections&gt;
      &lt;customer translate="label" module="customer"&gt;
          &lt;general&gt;
              &lt;groups&gt;
                  &lt;store_information&gt;
                      &lt;fields&gt;
                          &lt;company_name&gt;
                              &lt;label&gt;Company Name&lt;/label&gt;
                              &lt;frontend_type&gt;text&lt;/frontend_type&gt;
                              &lt;comment&gt;This will be included in Transactional Emails.&lt;/comment&gt;
                              &lt;sort_order&gt;31&lt;/sort_order&gt;
                              &lt;show_in_default&gt;1&lt;/show_in_default&gt;
                              &lt;show_in_website&gt;1&lt;/show_in_website&gt;
                              &lt;show_in_store&gt;1&lt;/show_in_store&gt;                    
                          &lt;/company_name&gt;
                      &lt;/fields&gt;
                      &lt;fields&gt;
                          &lt;gst_no&gt;
                              &lt;label&gt;GST No&lt;/label&gt;
                              &lt;frontend_type&gt;text&lt;/frontend_type&gt;
                              &lt;comment&gt;This will be included in Transactional Emails.&lt;/comment&gt;
                              &lt;sort_order&gt;32&lt;/sort_order&gt;
                              &lt;show_in_default&gt;1&lt;/show_in_default&gt;
                              &lt;show_in_website&gt;1&lt;/show_in_website&gt;
                              &lt;show_in_store&gt;1&lt;/show_in_store&gt;                    
                          &lt;/gst_no&gt;
                      &lt;/fields&gt;
                  &lt;/store_information&gt;
              &lt;/groups&gt;
          &lt;/general&gt;
      &lt;/customer&gt;
  &lt;/sections&gt;
  </code></pre>
  
  <p>
  MageCustom/GST/etc/config.xml</p>
  
  <pre><code>&lt;config&gt;
  &lt;adminhtml&gt;
      &lt;acl&gt;
          &lt;resources&gt;
              &lt;admin&gt;
                  &lt;children&gt;
                      &lt;system&gt;
                          &lt;children&gt;
                              &lt;config&gt;
                                  &lt;children&gt;
                                      &lt;customer&gt;
                                          &lt;title&gt;General&lt;/title&gt;
                                      &lt;/customer&gt;
                                  &lt;/children&gt;
                              &lt;/config&gt;
                          &lt;/children&gt;
                      &lt;/system&gt;
                  &lt;/children&gt;
              &lt;/admin&gt;
          &lt;/resources&gt;
      &lt;/acl&gt;
  &lt;/adminhtml&gt;
  </code></pre>
  
  <p></p>