Dockerfile: Adhere to spec

Dockerfile

@@ -1,6 +1,13 @@
 # Patch and build Olena from Git, then
 # Install OCR-D wrapper for binarization
 FROM ocrd/core:v2.62.0 AS base
+ARG VCS_REF
+ARG BUILD_DATE
+LABEL \
+    maintainer="https://github.com/OCR-D/ocrd_olena/issues" \
+    org.label-schema.vcs-ref=$VCS_REF \
+    org.label-schema.vcs-url="https://github.com/OCR-D/ocrd_olena" \
+    org.label-schema.build-date=$BUILD_DATE
 
 MAINTAINER OCR-D
 
@@ -26,7 +33,3 @@ RUN apt-get update && \
 
 WORKDIR /data
 VOLUME /data
-
-#ENTRYPOINT ["/usr/bin/ocrd-olena-binarize"]
-#CMD ["--help"]
-CMD ["/usr/bin/ocrd-olena-binarize", "--help"]