Merge pull request #600 from boucher/criu-readme

README example for using checkpoint/restore.

README.md

@@ -168,6 +168,38 @@ looking to see if `state.json` is in the root of the directory.
 You may also specify an alternate root place where
 the `container.json` file is read and where the `state.json` file will be saved.
 
+
+#### Checkpoint & Restore
+
+libcontainer now integrates [CRIU](http://criu.org/) for checkpointing and restoring containers.
+This let's you save the state of a process running inside a container to disk, and then restore
+that state into a new process, on the same machine or on another machine.
+
+`criu` version 1.5.2 or higher is required to use checkpoint and restore.
+If you don't already  have `criu` installed, you can build it from source, following the
+[online instructions](http://criu.org/Installation). `criu` is also installed in the docker image
+generated when building libcontainer with docker.
+
+To try an example with `nsinit`, open two terminals to the same busybox directory.
+In the first terminal, run a command like this one:
+```bash
+nsinit exec -- sh -c 'i=0; while true; do echo $i; i=$(expr $i + 1); sleep 1; done'
+```
+
+You should see logs printing to the terminal every second. Now, in the second terminal, run:
+```bash
+nsinit checkpoint --image-path=/tmp/criu
+```
+
+The logs in your first terminal will stop and the process will exit. Finally, in the second
+terminal, run the restore command:
+```bash
+nsinit restore --image-path=/tmp/criu
+```
+
+The process will resume counting where it left off and printing to the new terminal window.
+
+
 #### Future
 See the [roadmap](ROADMAP.md).