code: public function wifi($sType, $sSsid, $sPwd)
      {
          $this->sData .= 'WIFI:T:' . $sType . ';S' . $sSsid . ';' . $sPwd . "\n";
          return $this;
      }
docs: @param string $sType
  @param string $sSsid
  @param string $sPwd
  
  @return self