Update Dockerfile and README.md

Dockerfile

@@ -9,8 +9,6 @@ RUN \
   apt-get clean && \
   rm -rf /var/lib/apt/lists/*
 
-VOLUME ["/etc/apt/"]
-
 EXPOSE 80
 COPY setup.sh /setup.sh
 CMD /bin/bash setup.sh

README.md

@@ -3,10 +3,18 @@
 Base on Ubuntu, using Docker to construct your Apt mirror HTTP server
 
 ## Usage
+Using default [mirror.list!](mirror.list)
 ```
-docker run -d -p port_number:80 -v /path/your_mirror.list:/etc/apt/ seterrychen/apt-mirror-http-server
+docker run -v /path/data:/var/spool/apt-mirror \
+           -d -p port_number:80 seterrychen/apt-mirror-http-server
+```
+
+Using your mirror.list
+```
+docker run -v /path/data:/var/spool/apt-mirror \
+           -v /path/your/mirror.list:/etc/apt/mirror.list \
+           -d -p port_number:80 seterrychen/apt-mirror-http-server
 ```
 
 ## Note
-If you don't provide mirror.list file, the program will use default setting. 
 It will take time to download, then start http server. Using ``docker logs -f container-id`` to check the process.