Adding doc

Signed-off-by: Julien Barbier <write0@gmail.com>

docs/sources/reference/commandline/cli.md

@@ -642,8 +642,9 @@ is returned by the `docker attach` command to its caller too:
       -m, --memory=""          Memory limit for all build containers
       --memory-swap=""         Total memory (memory + swap), `-1` to disable swap
       -c, --cpu-shares         CPU Shares (relative weight)
-      --cpuset-cpus=""         CPUs in which to allow execution, e.g. `0-3`, `0,1`
       --cpuset-mems=""         MEMs in which to allow execution, e.g. `0-3`, `0,1`
+      --cpuset-cpus=""         CPUs in which to allow exection, e.g. `0-3`, `0,1`
+      --cgroup-parent=""       Optional parent cgroup for the container
 
 Builds Docker images from a Dockerfile and a "context". A build's context is
 the files located in the specified `PATH` or `URL`.  The build process can
@@ -862,6 +863,9 @@ you refer to it on the command line.
 > children) for security reasons, and to ensure repeatable builds on remote
 > Docker hosts. This is also the reason why `ADD ../file` will not work.
 
+`docker build` has a `--cgroup-parent` option that causes the containers used
+in the build to be run with this option.
+
 ## commit
 
     Usage: docker commit [OPTIONS] CONTAINER [REPOSITORY[:TAG]]