Update secret key instructions to use asciinema gen_secret
Update secret key instructions to use asciinema gen_secret

asciinema/asciinema-server,asciinema/asciinema-server,asciinema/asciinema-server,asciinema/asciinema.org,asciinema/asciinema-server,asciinema/asciinema.org,asciinema/asciinema.org,asciinema/asciinema.org