Add option for building pull requests

README.md

@@ -80,3 +80,16 @@ with:
   password: ${{ secrets.DOCKER_PASSWORD }}
   cache: true
 ```
+
+### pull_requests
+Use `pull_requests` if you would like to publish pull requests.  
+The images will be published under 'pr{NUMBER_OF_PR}{ACTION_IN_REF}'  
+> CAUTION: Only activate this option, when you are really sure, that nobody will be able to do something bad in your name within the PR.
+
+```yaml
+with:
+  name: myDocker/repository
+  username: ${{ secrets.DOCKER_USERNAME }}
+  password: ${{ secrets.DOCKER_PASSWORD }}
+  pull_requests: true
+```