refined dockerfile

Dockerfile

@@ -1,5 +1,13 @@
 FROM alpine
-MAINTAINER Philipp C. Heckel <philipp.heckel@gmail.com>
+
+LABEL org.opencontainers.image.authors="philipp.heckel@gmail.com"
+LABEL org.opencontainers.image.url="https://ntfy.sh/"
+LABEL org.opencontainers.image.documentation="https://docs.ntfy.sh/"
+LABEL org.opencontainers.image.source="https://github.com/binwiederhier/ntfy"
+LABEL org.opencontainers.image.vendor="Philipp C. Heckel"
+LABEL org.opencontainers.image.licenses="Apache-2.0, GPL-2.0"
+LABEL org.opencontainers.image.title="ntfy"
+LABEL org.opencontainers.image.description="Send push notifications to your phone or desktop using PUT/POST"
 
 COPY ntfy /usr/bin