Add more comments in Dockerfile

Dockerfile

@@ -38,19 +38,24 @@ RUN cd /go/src/github.com/mholt/caddy/caddy \
 #
 FROM debian:stable as compress
 
+# curl, tar
 RUN apt-get update && apt install -y --no-install-recommends \
     tar \
     xz-utils \
     curl \
     ca-certificates
 
+# get official upx binary
 RUN curl --silent --show-error --fail --location -o - \
     "https://github.com/upx/upx/releases/download/v3.94/upx-3.94-amd64_linux.tar.xz" \
     | tar --no-same-owner -C /usr/bin/ -xJ \
     --strip-components 1 upx-3.94-amd64_linux/upx
 
+# copy and compress
 COPY --from=build /go/bin/caddy /usr/bin/caddy
 RUN /usr/bin/upx --ultra-brute /usr/bin/caddy
+
+# test
 RUN /usr/bin/caddy -version
 
 
@@ -59,17 +64,23 @@ RUN /usr/bin/caddy -version
 #
 FROM scratch
 
+# labels
 LABEL org.label-schema.vcs-url="https://github.com/productionwentdown/caddy"
 LABEL org.label-schema.version=${version}
 LABEL org.label-schema.schema-version="1.0"
 
+# copy caddy binary and ca certs
 COPY --from=compress /usr/bin/caddy /bin/caddy
 COPY --from=compress /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/ca-certificates.crt
+
+# copy default caddyfile
 COPY Caddyfile /etc/Caddyfile
 
+# set default caddypath
 ENV CADDYPATH=/etc/.caddy
 VOLUME /etc/.caddy
 
+# serve from /srv
 WORKDIR /srv
 COPY index.html /srv/index.html