add check

README.md

@@ -18,9 +18,26 @@ A required argument, this represents the "base" image you want to check against.
 As this is based on `skopeo`, it expects a string representing a container, and following a certain format
 (e.g. `docker://rust:slim-buster`). For more information, see [the `skopeo` README](https://github.com/containers/skopeo#skopeo-).
 
-### Outputs
+#### `derived-image`
 
 A required argument, this represents the "derived" image you want to check.
 
 As this is based on `skopeo`, it expects a string representing a container, and following a certain format
 (e.g. `docker://rust:slim-buster`). For more information, see [the `skopeo` README](https://github.com/containers/skopeo#skopeo-).
+
+### Outputs
+
+#### `differs`
+
+The action returns either `true` or `false`, indicating if the derived image differs from the base image (e.g. if derived does not contain the base, it returns `true`).
+
+## Example
+
+```yaml
+- name: Run
+id: run
+uses: ClementTsang/docker-check-base-image-diff@v0.0.1-alpha
+with:
+    base-image: docker://rust:slim-buster
+    derived-image: docker://ghcr.io/clementtsang/cargo-deb-arm
+```