Use :sh: in sshd example

[hilbix]

Currently :/bin/sh:-c: is used in the sshd example in README.md.
So this probably use :sh: instead.

[hilbix]

For this I need to test on some Win11 WSL again - currently I have no such environment ready

Of course I use WSL 2. But not this sshd was designed for Win10 WSL 1.

As this is just cosmetic, I just file this issue as a reminder