Add missing revision labels for arm builds

Dockerfile.armhf

@@ -61,6 +61,13 @@ ENV OPENVPN_USERNAME=**None** \
 
 HEALTHCHECK --interval=1m CMD /etc/scripts/healthcheck.sh
 
+# Add labels to identify this image and version
+ARG REVISION
+# Set env from build argument or default to empty string
+ENV REVISION=${REVISION:-""}
+LABEL org.opencontainers.image.source=https://github.com/haugene/docker-transmission-openvpn
+LABEL org.opencontainers.image.revision=$REVISION
+
 # Compatability with https://hub.docker.com/r/willfarrell/autoheal/
 LABEL autoheal=true