Tidying up.

Dockerfile

 FROM cznic/knot-resolver
 RUN echo '@testing http://dl-cdn.alpinelinux.org/alpine/edge/testing' >> /etc/apk/repositories && \
-    apk add --update \
+    apk add --update --no-cache \
         dma@testing \
         iproute2 \
         knot-utils \
         mailx \
-        mtr \
-    && \
-    rm -rf /var/cache/apk/* /tmp/* /var/tmp/*
+        mtr
 COPY entrypoint /entrypoint
+WORKDIR /
 ENTRYPOINT [ "/entrypoint" ]
 CMD [ "bash", "--login" ]

README.md

@@ -5,4 +5,4 @@ https://www.shore.co.il/blog/resolver/.
 
 ## Usage
 
-    docker run -it adarnimrod/resolver
+    docker run --rm -it adarnimrod/resolver