Dockerfile: Removes arguable comments

- user data could be stored in any kind of volume
  - using a mounted one is often not recommendable
- there are other means to publish a service like HTTP reverse proxies
- the CMD directive can't and shouldn't be used to expose behaviour
  - in fact, the value is required by the previous directive

Dockerfile

@@ -1,14 +1,16 @@
+# This file is intended to be used apart from the containing source code tree.
+
 FROM python:3-alpine
 
 # Version of Radicale (e.g. 3.0.x)
 ARG VERSION=master
-# Persistent storage for data (Mount it somewhere on the host!)
+# Persistent storage for data
 VOLUME /var/lib/radicale
 # Configuration data (Put the "config" file here!)
 VOLUME /etc/radicale
-# TCP port of Radicale (Publish it on a host interface!)
+# TCP port of Radicale
 EXPOSE 5232
-# Run Radicale (Configure it here or provide a "config" file!)
+# Run Radicale
 CMD ["radicale", "--hosts", "0.0.0.0:5232"]
 
 RUN apk add --no-cache ca-certificates openssl \