Don't declare /dns as a volume.

For letsencrypt-lexicon to extend this, it needs to be able to
place its hook in the right place. If /dns is a volume then it's
auto-created and mounted and any changes made in the Dockerfile are
discarded.

Dockerfile

@@ -9,7 +9,7 @@ RUN apt-get update \
 COPY letsencrypt.sh run.sh config.sh /
 RUN chmod +x /run.sh /letsencrypt.sh
 
-VOLUME ["/letsencrypt", "/dns"]
+VOLUME ["/letsencrypt"]
 
 ENTRYPOINT ["/bin/bash"]
 CMD ["/run.sh"]

README.md

@@ -42,8 +42,8 @@ the update. See the documentation for
 [letsencrypt.sh](https://github.com/lukas2511/letsencrypt.sh) for details
 on the arguments it takes.
 
-The container expects an executable at `/dns/hook`, and exposes the 
-`/dns` volume for you to mount.
+The container expects an executable at `/dns/hook`, so you'll need to
+mount the `/dns` folder or `/dns/hook` file when running the container.
 
 ### Other configuration