Add app version in footer

.env

@@ -0,0 +1,2 @@
+REACT_APP_VERSION=$npm_package_version
+REACT_APP_NAME=$npm_package_name

src/Footer.js

@@ -12,6 +12,7 @@ export default function Footer(props) {
 					<Link to="/privacy">Privacy policy</Link>
 				</>
 			}
+			<span>v{process.env.REACT_APP_VERSION}</span>
 		</footer>
 	)
 }