Add 404 Page
Adding a 404 page is easy. Simply create a page that matches
often you’ll just want to create a React component page at
Gatsby ensures that your 404 page is outputted as
404.html as many static
hosting platforms default to using this as your 404 error page. If you’re
hosting your site another way, you’ll need to setup a custom rule to serve
this file for 404 errors.