verify Windows compatibility

[MikiDi]

The usual tail /dev/null trick to keep a container running doesn't seem to work with Docker for Windows. The container starts, which makes the startup check succeed, but by the time mu cli wants to do something with it, it is no longer running (stops running within a second or so).

In case Windows isn't supported, a little notice in the Readme might be advised.

cc @tdn

[tdn]

haven't had a chance to take a deep dive into this yet. Will update later when I can try some fixes