docs: Add Hyper-V documentation

Signed-off-by: Rolf Neugebauer <rolf.neugebauer@docker.com>

docs/platform-hyperv.md

@@ -0,0 +1,76 @@
+# LinuxKit with Hyper-V
+
+LinuxKit supports running LinuxKit created VMs on Hyper-V on Microsoft
+Windows. `linuxkit` must be run from an elevated command prompt,
+typically a elevated Powershell and utilises Powershell scripting to
+manage the Hyper-V VMs.
+
+
+Example:
+```sh
+linuxkit.exe run -disk size=1 linuxkit-efi.iso
+```
+
+The Hyper-V VM, by default, is named after the prefix of the ISO, ie
+with `.iso` and `-efi` stripped. Note, You may only have one VM for a
+given name.  You can specify an alternative name using the `-name`
+command-line option.
+
+
+## Boot
+
+Currently, the Hyper-V backend only supports booting EFI ISO images
+created with LinuxKit. `linuxkit` create a Generation 2 VM and
+disables secure EFI boot for booting.
+
+In the future, we may add support for legacy BIOS ISOs, booting from
+disks, and enable secure boot.
+
+
+## Console
+
+The serial port of the VM is configured to redirect to a Named Pipe,
+and when the `linuxkit` command is executed an interactive console is
+provided in the same window. The serial console may also be redirected
+to a file.
+
+**Note:** The connection to the Named Pipe sometimes seems to be a bit
+racey, though the code itself should be fine. You may have to try
+again if the connection to the serial console fails.
+
+If the main console is configured within the VM, one can also connect
+to it using the Hyper-V manager, or from the command-line:
+```sh
+vmconnect.exe localhost linuxkit
+```
+
+## Disks
+
+The Hyper-V backend supports multiple disks to be attached to the VM
+using the standard `linuxkit` `-disk` syntax. While Hyper-V typically
+stores disk images under a default location, if the VM is created with
+`linuxkit`, by default, new disks are created in the current
+directory.
+
+
+## Networking
+
+By default, the Hyper-V backend will try to find an external switch
+configured by the user and use this for network connectivity for the
+VM.  This means that DHCP will be provided by the normal DHCP server
+on your network. Depending on your firewall settings, you may be able
+to access the VM directly via its IP address.
+
+Alternatively, you can specify a Hyper-V switch to use using the
+`-switch` command-line option. In this case it is the user's
+responsibility to provide a DHCP server or to configure the VM's IP
+address by some other means.
+
+
+## Integration services and Metadata
+
+LinuxKit does not yet have packages for Hyper-V integration agents
+(KVP and VSS daemons). We plan to add them soon.
+
+The Hyper-V backend currently does not support passing
+metadata/userdata to the VM.