Improves Page Not Found UX (#9613)

* Updates Page Not Found UX with Link

* Adds Link to 404.js

* Updates code indentation

Co-Authored-By: pranshuchittora <pranshuchittora17@gmail.com>

* Updates routes from './' to '/'

Co-Authored-By: pranshuchittora <pranshuchittora17@gmail.com>

www/src/pages/404.js

@@ -1,13 +1,20 @@
 import React from "react"
 import Container from "../components/container"
 import Layout from "../components/layout"
+import { Link } from "gatsby"
 
 class FourOhFour extends React.Component {
   render() {
     return (
       <Layout location={this.props.location}>
         <Container>
           <h1>Page not found</h1>
+          <p>
+            Oops! The page you are looking for has been removed or relocated.
+          </p>
+          <Link to="/">
+            <p>Go Back</p>
+          </Link>
         </Container>
       </Layout>
     )