How can I generate ECH keys for testing with nginx? #26

I am following the March 2023 steps here:

I've generated some fake CA / website certs via make-example-ca.sh , which seems to be fine. However if I try testnginx-draft-13.sh , I get the following:

Executing:  /home/ubuntu/code/nginx/objs/nginx -c /home/ubuntu/code/openssl-for-nginx/esnistuff/nginxmin-draft-13.conf
nginx: [emerg] load_echkeys, error opening /home/ubuntu/code/openssl-for-nginx/esnistuff/echkeydir at 1463
nginx: [emerg] Hey some bad ech stuff happened at 1544

I tried to search around a bit, but not too sure how to populate this directory with the ECH keys. Any advice would be great.