feat(Not Found): Add not found page (#10)

src/pages/NotFound.tsx

@@ -0,0 +1,30 @@
+import { makeStyles, Typography } from "@material-ui/core";
+import React from "react";
+import { Link } from "react-router-dom";
+
+const useStyle = makeStyles(() => ({
+	container: {
+		position: "absolute",
+		top: "50%",
+		left: "50%",
+		transform: "translate(-50%, -50%)",
+		textAlign: "center"
+	}
+}));
+
+const NotFound: React.FC = () => {
+	const classes = useStyle();
+	return (
+		<div className={classes.container}>
+			<Typography variant="h1" style={{ fontWeight: "bold" }}>
+				404
+			</Typography>
+			<Typography variant="h6" gutterBottom>
+				This page could not be found
+			</Typography>
+			<Link to="/">Back to home</Link>
+		</div>
+	);
+};
+
+export default NotFound;

src/routes/index.tsx

@@ -1,3 +1,4 @@
+import NotFound from "pages/NotFound";
 import React, { Suspense } from "react";
 import { Route, Switch } from "react-router-dom";
 
@@ -9,7 +10,8 @@ const AppRouter: React.FC = () => {
 		<Suspense fallback="loading...">
 			<Switch>
 				<Route path="/secret/:token" exact component={ShowSecret} />
-				<Route path="/" component={CreateSecret} />
+				<Route path="/" exact component={CreateSecret} />
+				<Route path="*" component={NotFound} />
 			</Switch>
 		</Suspense>
 	);