Correct Go version in README

Upgrade to k6 v0.47.0 (#16)

With this commit we upgrade the k6 dependency to v0.47.0 and also
increase the Go version to 1.20.

Meet k6 registry requirements (#9)

With this commit we:

* Simplify the docker-compose file and improve docs
* Move the example script to the required directory
* Upgrade to the most recent version of k6

Relates #8