Document the digest output

README.md

@@ -42,6 +42,7 @@ If you would like to publish the image to other registries, these actions might
 
 `tag` is the tag, which was pushed  
 `snapshot-tag` is the tag that is generated by the [snapshot-option](https://github.com/elgohr/Publish-Docker-Github-Action#snapshot) and pushed  
+`digest` is the digest of the image, which was pushed  
 
 ## Optional Arguments
 

action.yml

@@ -40,6 +40,8 @@ outputs:
     description: 'Is the tag, which was pushed'
   snapshot-tag:
     description: 'Is the tag that is generated by the snapshot-option and pushed'
+  digest:
+    description: 'Is the digest of the image, which was pushed'
 runs:
   using: 'docker'
   image: 'Dockerfile'