docs: mention OCI-compliant metadata

Author: joonas-fi

README.md

@@ -19,6 +19,8 @@ Features
 --------
 
 - [Log line grouping](https://user-images.githubusercontent.com/630151/194755923-d81df7cf-1e80-40b8-b1b3-886d973fdb4d.mp4) in GitHub actions
+- Automatically adds [OCI-compliant metadata](https://github.com/opencontainers/image-spec/blob/main/annotations.md)
+  to built containers. ([Example](https://hub.docker.com/r/joonas/hellohttp/tags), click "latest")
 
 
 Additional documentation