Update Custom error page with nginx

Custom-error-page-with-nginx.md

@@ -34,6 +34,12 @@ Now edit the site's nginx config:
 sudo nano /etc/nginx/sites-available/default
 ```
 
+Add in the following line inside `server { ... }`
+
+```
+error_page 502 /502.html;
+```
+
 Add in the following section after `location / { ... }`
 
 ```