Add recommended proxy buffer config to example nginx config for local HTTPS.

I found that this was necessary for the asset GeoJSON Views to prevent 502 Bad Gateway.

docs/development/environment/https.md

@@ -35,6 +35,9 @@ http {
       proxy_set_header X-Forwarded-Host $http_host;
       proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
       proxy_set_header X-Forwarded-Proto $scheme;
+      proxy_buffer_size 128k;
+      proxy_buffers 4 256k;
+      proxy_busy_buffers_size 256k;
       proxy_pass http://www;
     }
   }