Docs feedback: Kaniko guide should describe how to handle custom certificates

The https://docs.gitlab.com/ce/ci/docker/using_kaniko.html page should describe how to handle registries which have a certificate signed by a custom CA.

$ /kaniko/executor --context $CI_PROJECT_DIR --dockerfile $CI_PROJECT_DIR/Dockerfile --no-push
INFO[0000] Downloading base image registry.gitlab.example.com/group/docker-image 
error building image: getting stage builder for stage 0: Get https://registry.gitlab.example.com/v2/: x509: certificate signed by unknown authority

I worked around it by adding the Root CA cert in the before_script:

  before_script:
    - echo "{\"auths\":{\"$CI_REGISTRY\":{\"username\":\"$CI_REGISTRY_USER\",\"password\":\"$CI_REGISTRY_PASSWORD\"}}}" > /kaniko/.docker/config.json
    - |
      echo "-----BEGIN CERTIFICATE-----
      ...
      -----END CERTIFICATE-----" >> /kaniko/ssl/certs/ca-certificates.crt