docs: move checkpoint/restore doc from experimental into reference

This allows this information to be read from docs.docker.com.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

docs/reference/commandline/checkpoint.md

@@ -1,6 +1,13 @@
-# Docker Checkpoint & Restore
+---
+title: docker checkpoint
+description: "The checkpoint command description and usage"
+keywords: experimental, checkpoint, restore, criu
+experimental: true
+---
 
-Checkpoint & Restore is a new feature that allows you to freeze a running
+## Description
+
+Checkpoint and Restore is an experimental feature that allows you to freeze a running
 container by checkpointing it, which turns its state into a collection of files
 on disk. Later, the container can be restored from the point it was frozen.
 
@@ -9,16 +16,16 @@ external dependency of this feature. A good overview of the history of
 checkpoint and restore in Docker is available in this
 [Kubernetes blog post](https://kubernetes.io/blog/2015/07/how-did-quake-demo-from-dockercon-work/).
 
-## Installing CRIU
+### Installing CRIU
 
 If you use a Debian system, you can add the CRIU PPA and install with apt-get
 [from the criu launchpad](https://launchpad.net/~criu/+archive/ubuntu/ppa).
 
-Alternatively, you can [build CRIU from source](http://criu.org/Installation).
+Alternatively, you can [build CRIU from source](https://criu.org/Installation).
 
 You need at least version 2.0 of CRIU to run checkpoint/restore in Docker.
 
-## Use cases for checkpoint & restore
+### Use cases for checkpoint & restore
 
 This feature is currently focused on single-host use cases for checkpoint and
 restore. Here are a few:
@@ -33,7 +40,7 @@ migration of a server from one machine to another. This is possible with the
 current implementation, but not currently a priority (and so the workflow is
 not optimized for the task).
 
-## Using checkpoint & restore
+### Using checkpoint & restore
 
 A new top level command `docker checkpoint` is introduced, with three subcommands:
 - `create` (creates a new checkpoint)
@@ -44,35 +51,40 @@ Additionally, a `--checkpoint` flag is added to the container start command.
 
 The options for checkpoint create:
 
+```console
 Usage:  docker checkpoint create [OPTIONS] CONTAINER CHECKPOINT
 
 Create a checkpoint from a running container
 
   --leave-running=false    Leave the container running after checkpoint
   --checkpoint-dir         Use a custom checkpoint storage directory
+```
 
 And to restore a container:
 
+```console
 Usage:  docker start --checkpoint CHECKPOINT_ID [OTHER OPTIONS] CONTAINER
+```
 
+Example of using checkpoint & restore on a container:
 
-A simple example of using checkpoint & restore on a container:
-
+```console
 $ docker run --security-opt=seccomp:unconfined --name cr -d busybox /bin/sh -c 'i=0; while true; do echo $i; i=$(expr $i + 1); sleep 1; done'
-    > abc0123
+abc0123
 
 $ docker checkpoint create cr checkpoint1
 
 # <later>
 $ docker start --checkpoint checkpoint1 cr
-    > abc0123
+abc0123
+```
 
 This process just logs an incrementing counter to stdout. If you `docker logs`
 in between running/checkpoint/restoring you should see that the counter
 increases while the process is running, stops while it's checkpointed, and
 resumes from the point it left off once you restore.
 
-## Current limitation
+### Known limitations
 
 seccomp is only supported by CRIU in very up to date kernels.
 
@@ -80,9 +92,10 @@ External terminal (i.e. `docker run -t ..`) is not supported at the moment.
 If you try to create a checkpoint for a container with an external terminal, 
 it would fail:
 
+```console
 $ docker checkpoint create cr checkpoint1
 Error response from daemon: Cannot checkpoint container c1: rpc error: code = 2 desc = exit status 1: "criu failed: type NOTIFY errno 0\nlog file: /var/lib/docker/containers/eb62ebdbf237ce1a8736d2ae3c7d88601fc0a50235b0ba767b559a1f3c5a600b/checkpoints/checkpoint1/criu.work/dump.log\n"
 
 $ cat /var/lib/docker/containers/eb62ebdbf237ce1a8736d2ae3c7d88601fc0a50235b0ba767b559a1f3c5a600b/checkpoints/checkpoint1/criu.work/dump.log
 Error (mount.c:740): mnt: 126:./dev/console doesn't have a proper root mount
-
+```

experimental/README.md

@@ -11,8 +11,6 @@ please feel free to provide any feedback on these features you wish.
 
 ## Use Docker experimental
 
-Experimental features are now included in the standard Docker binaries as of
-version 1.13.0.
 To enable experimental features, start the Docker daemon with the
 `--experimental` flag or enable the daemon flag in the
 `/etc/docker/daemon.json` configuration file:
@@ -39,5 +37,5 @@ Checkpoint and restore support for Containers.
 Metrics (Prometheus) output for basic container, image, and daemon operations.
 
  * [External graphdriver plugins](../docs/extend/plugins_graphdriver.md)
- * [Checkpoint & Restore](checkpoint-restore.md)
+ * [Checkpoint & Restore](../docs/reference/commandline/checkpoint-restore.md)
  * [Docker build with --squash argument](../docs/reference/commandline/build.md#squash-an-images-layers---squash-experimental)