docs: add disclaimer

.github/actions/create-checkbox-canary-test-job/action.yaml

@@ -16,6 +16,9 @@ runs:
  using: "composite"
  steps:
  - id: job-creator
+ # This is purely a proof-of-concept. You shouldn't handle inline bash scripts in Github actions.
+ # Please just don't, it won't end well. This is normally the place to feed the action inputs to
+ # a dedicated tool that generates the Checkbox launcher.
  shell: bash
  run: |
  OUTPUT_PATH=${{ github.workspace }}/job.yaml