WSL and accessing shared folders in guest (windows 10)

I have a windows host and a windows guest. I am using wsl, ubuntu bash on windows.

I have a shared folder in the host. Outside of wsl, I can access it in the guest. But in wsl, I cannot access it in guest. Note Wsl now supports shared folders:

  https://blogs.msdn.microsoft.com/wsl/2017/04/18/file-system-improvements-to-the-windows-subsystem-for-linux/

How can I get this to work?

thanks.