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README.md

@@ -1,5 +1,26 @@
 # docker-check-base-image-diff
 
-A Github Action that checks for Docker base image updates. Leverages skopeo and jq.
+A Github Action that checks whether a derived image does not consist of a base image. Leverages
+[`skopeo`](https://github.com/containers/skopeo) and [`jq`](https://stedolan.github.io/jq/).
 
 Based on [lucacome's docker-image-update-checker](https://github.com/lucacome/docker-image-update-checker).
+
+## Usage
+
+Note that this action _assumes_ that `skopeo` is installed; this appears to be true for GitHub's Ubuntu runners.
+
+### Inputs
+
+#### `base-image`
+
+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
+
+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-).