For local development start a pebble server:
./pebble/run
Then add the following to your /etc/hosts
127.0.0.1 example.com
To run the ACME client to issue and install a certificate:
go run ./src http01 --dir https://localhost:14000/dir --record 127.0.0.1 --domain example.com
To verify that it worked visit https://localhost:5001 or run:
openssl s_client -showcerts -connect example.com:5001 </dev/null