Added a bit of a readme

README.md

@@ -1,3 +1,22 @@
 # push-to-dokku
 
-Action to push to Dokku
+Action to push a remote repository to Dokku.
+
+## Usage
+
+```
+uses: https://lmika.dev/actions/push-to-dokku@v1
+with:
+  app: dokku-app-name
+  host: dokku-host
+  private-key: SSH key
+```
+
+Parameters are:
+
+- `host`: hostname of the Dokku instance to push the application to.
+- `app`: the Dokku application name.
+- `private-key`: the private SSH key
+
+This action will write the private key to the .ssh instance and will push to the remote repository as the `dokku`
+user. Both the source and target branch must be `main`.