Add WSL as another use case for psusan.

I've just spent the afternoon playing with it (rather belatedly - this
is the first time I've tried it out since it was first announced!),
and quickly decided that on the one hand it looks quite useful, but on
the other hand, running it in a Windows console is not for me and I'd
prefer to talk to it via PuTTY and psusan, for nicer copy-paste
controls and the ability to forward Pageant into it.

That turns out to be very easy and (I think) useful, so in it goes as
another psusan use case.

doc/man-psusan.but

@@ -201,6 +201,36 @@ PuTTY session that starts up a clean UML instance when you run it, and
 (if you enabled connection sharing) further instances of the same
 session will connect to the same instance again.
 
+\S2{psusan-manpage-examples-wsl} Windows Subsystem for Linux
+
+On Windows, the default way to use WSL is to run the \cw{wsl} program,
+or one of its aliases, in a Windows console, either by launching it
+from an existing command prompt, or by using a shortcut that opens it
+in a fresh console. This gives you a Linux terminal environment, but
+in a Windows console window.
+
+If you'd prefer to interact with the same environment using PuTTY as
+the terminal (for example, if you prefer PuTTY's mouse shortcuts for
+copy and paste), you can set it up by installing \cw{psusan} in the
+Linux environment, and then setting up a PuTTY saved session that
+talks to it. A nice way to do this is to use the name of the WSL
+distribution as the \q{host name}:
+
+\b set the local proxy command to \cq{wsl -d %host
+/usr/local/bin/psusan} (or wherever you installed \cw{psusan} in the
+Linux system)
+
+\b enter the name of a particular WSL distribution in the host name
+box. (For example, if you installed WSL Debian in the standard way
+from the Windows store, this will just be \q{Debian}.)
+
+\b set the protocol to \q{Bare ssh-connection}, as usual.
+
+Like all the other examples here, this also permits you to forward
+ports in and out of the WSL environment (e.g. expose a WSL2 network
+service through the hypervisor's internal NAT), forward Pageant into
+it, and so on.
+
 \S2{psusan-manpage-examples-schroot} \cw{schroot}
 
 Another example of a container-like environment is the alternative