Add more documentation

README.md

@@ -19,6 +19,27 @@ This is not just a Raspian Docker image, it's a full ARM based Raspberry Pi virt
 docker run -it lukechilds/dockerpi
 ```
 
+By default all filesystem changes will lost on shutdown. You can persist filesystem changes between reboots by mounting the `/sdcard` volume on your host:
+
+```
+docker -v $HOME/.dockerpi:/sdcard run -it lukechilds/dockerpi
+```
+
+If you have a specific image you want to mount you can mount it at `/sdcard/filesystem.img`:
+
+```
+docker -v /2019-09-26-raspbian-buster-lite.img:/sdcard/filesystem.img run -it lukechilds/dockerpi
+```
+
+If you only want to mount your own image, you can download a much slimmer VM only Docker container that doesn't contain the Raspbian filesystem image:
+
+[![Docker Image Size](https://badgen.net/docker/size/lukechilds/dockerpi/latest/amd64?icon=docker&label=lukechilds/dockerpi:latest)](https://hub.docker.com/r/lukechilds/dockerpi/tags?name=latest)
+[![Docker Image Size](https://badgen.net/docker/size/lukechilds/dockerpi/vm/amd64?icon=docker&label=lukechilds/dockerpi:vm)](https://hub.docker.com/r/lukechilds/dockerpi/tags?name=vm)
+
+```
+docker -v /2019-09-26-raspbian-buster-lite.img:/sdcard/filesystem.img run -it lukechilds/dockerpi:vm
+```
+
 ## Build
 
 Build this image yourself by checking out this repo, `cd` ing into it and running: