Add SideBarFooter to SideBar

SideBar.js

/*...*/
import {SideBarFooter} from './SideBarFooter/SideBarFooter';

export class SideBar extends React.Component {
  render() {
    return (
      <Menu borderless vertical stackable fixed='left' className='side-nav'>
        {/*rest unchanged*/}
        <SideBarItem label='Send feedback' icon='comment'/>
        <Divider/>
        <SideBarFooter/>
      </Menu>
    );
  }
}