Initial implementation

Update README.md

This adds basic directory mount support for job containers. As any path on the host
is already accessible from the container, the concept of volume mounts is a bit funny
for job containers. However, it still makes sense to treat the volume mount point where
the container image is mounted as where most things should be found regarding the container.

The manner in which this is done is by appending the container mount path for the volume to
where the rootfs volume is mounted on the host and then symlinking it.

So:
Container rootfs volume path = "C:\C\123456789abcdefgh\"

Example #1
--------------
{
    "host_path": "C:\mydir"
    "container_path": "\dir\in\container"
}

"C:\mydir" would be symlinked to "C:\C\123456789abcdefgh\dir\in\container"

Example #2
---------------
Drive letters will be stripped
{
    "host_path": "C:\mydir"
    "container_path": "C:\dir\in\container"
}
"C:\mydir" would be symlinked to "C:\C\123456789abcdefgh\dir\in\container"

Signed-off-by: Daniel Canter <dcanter@microsoft.com>

This adds basic directory mount support for job containers. As any path on the host
is already accessible from the container, the concept of volume mounts is a bit funny
for job containers. However, it still makes sense to treat the volume mount point where
the container image is mounted as where most things should be found regarding the container.

The manner in which this is done is by appending the container mount path for the volume to
where the rootfs volume is mounted on the host and then symlinking it.

So:
Container rootfs volume path = "C:\C\123456789abcdefgh\"

Example microsoft#1
--------------
{
    "host_path": "C:\mydir"
    "container_path": "\dir\in\container"
}

"C:\mydir" would be symlinked to "C:\C\123456789abcdefgh\dir\in\container"

Example microsoft#2
---------------
Drive letters will be stripped
{
    "host_path": "C:\mydir"
    "container_path": "C:\dir\in\container"
}
"C:\mydir" would be symlinked to "C:\C\123456789abcdefgh\dir\in\container"

Signed-off-by: Daniel Canter <dcanter@microsoft.com>