fix docker nixery example in the introducing spindle blog post #1

the current example fails with a fun very deeply nested error

$ docker run nixery.dev/bash/hello-go hello
docker: Error response from daemon: failed to create task for container: failed to create shim task: OCI runtime create failed: runc create failed: unable to start container process: error during container init: exec: "hello": executable file not found in $PATH

Run 'docker run --help' for more information

(first pr on tangled 🥳)