message: docs(GSS Codes): Add docs for LSOA and MSOA codes
diff: </td>
  <td>The NUTS 3 code associated with the postcode.</td>
  </tr>
  + <tr>
  + <td>
  + codes.lau2 <br />
  + <code>string|null</code>
  + </td>
  + <td>The LAU2 code associated with the postcode.</td>
  + </tr>
  + <tr>
  + <td>
  + codes.lsoa <br />
  + <code>string|null</code>
  + </td>
  + <td>See description of <code>lsoa</code> field.</td>
  + </tr>
  + </tr>
  + <tr>
  + <td>
  + codes.msoa <br />
  + <code>string|null</code>
  + </td>
  + <td>See description of <code>msoa</code> field.</td>
  + </tr>
  </tbody>
  </table>
  