docs: improve README

README.md

@@ -1,3 +1,44 @@
 # attic-action
 
-Cache Nix derivations with [attic](https://github.com/zhaofengli/attic).
+Cache Nix derivations with [Attic](https://github.com/zhaofengli/attic).
+
+## Usage
+
+Configure your attic instance with an endpoint, a cache, and a token that can read from and write to the cache. Then, add this step to a workflow job after Nix is installed:
+
+```yaml
+- name: Setup Attic cache
+  uses: ryanccn/attic-action@v0
+  with:
+    endpoint: ${{ secrets.ATTIC_ENDPOINT }}
+    cache: ${{ secrets.ATTIC_CACHE }}
+    token: ${{ secrets.ATTIC_TOKEN }}
+```
+
+## Inputs
+
+### `endpoint`
+
+The Attic endpoint. This is the URL without the cache name.
+
+### `cache`
+
+The name of the Attic cache.
+
+### `token`
+
+The authorization token to provide to Attic (**optional**).
+
+### `skip-push`
+
+Disable pushing new derivations to the cache automatically at the end of the job (**default is false**).
+
+This requires you to invoke `attic push <cache>` with the paths you want to push to the cache manually.
+
+## Outputs
+
+None
+
+## License
+
+MIT