Document the gitlab-runner-helper needed for cache to work
VERY IMPORTANT: For cache to work, the
gitlab-runner-helperbinary is required. For
kubernetesexecutors we're resolving this by providing helper image that is used for
shellexecutor - if installed from our package - the binary is installed together with Runner main binary. For any other installation (e.g. from source, by downloading binaries from our S3 release bucket) helper binary needs to be installed manually to make cache (and artifacts!) working. When using
parallelsexecutors, even if installed from our DEB/RPM packages, the helper binary needs to be installed on the SSH host/inside of the VM image to make cache (and artifacts!) working.