Merge branch 'hustewart-update-readme' into 'master'

docs: add testing section to README

See merge request https://gitlab.com/gitlab-org/cluster-integration/auto-deploy-image/-/merge_requests/345



Merged-by: Tiger Watson <twatson@gitlab.com>
Approved-by: Tiger Watson <twatson@gitlab.com>
Co-authored-by: hustewart <hustewart@gitlab.com>