add custom 404 page

docker/nginx.conf

@@ -63,5 +63,11 @@ http {
       # Serve the file directly from disk
       try_files $uri $uri/ =404;
     }
+
+    # Fallback 404 page
+    location = /404.html {
+      try_files $uri $uri/ =404;
+    }
+    error_page 404 /404.html;
   }
 }