review: Add README for image gathering

scripts/README.md

@@ -0,0 +1,24 @@
+# Utility Script
+
+This directory contains helper scripts for Charmed Kubeflow, during CI and not only.
+
+## Gather images used by a bundle
+
+You can get a list of all the OCI images used by the bundle by running the following command:
+```bash
+python3 scripts/get-all-images.py \
+    --append-images tests/airgapped/ckf-1.8-testing-images.txt \
+    releases/1.8/stable/kubeflow/bundle.yaml \
+    > images-all.txt
+```
+
+The script will gather the images in the following way:
+1. For each `application` in the provided `bundle.yaml` file:
+2. detect if it's owned by us or another team (by looking at the `_github_dependency_repo_name` and such metadata)
+3. clone its repo, by looking at `_github_repo_name` and such metadata
+4. If owned by another team: only parse it's `metadata.yaml` and look for `oci-resources`
+5. If owned by us: run the `tools/get-images.sh` script the repo **must** have
+6. If a repo does not have `tools/get-images.sh` (i.e. kubeflow-roles) then the script should skip the repo
+7. If the `get-images.sh` script either fails (return code non zero) or has error logs then the script should **fail**
+8. Aggregate the outputs of all `get-images.sh` scripts to one output
+9. If user passed an argument `--append-images` then the script will amend a list of images we need for airgap testing