Hint at Host support for ssh_config (#133)

The `ssh_config` state supports generating `Host` sections, but it is
buried in the source. By default, options are simply dumped in the
configuration file; without any `Host` directive.

This patch hints (and, actually, encourages) users to use `Host`
sections by updating the pillar example to use the `Hosts` directive
with the `*` pattern.

pillar.example

@@ -143,6 +143,8 @@ sshd_config:
 # machine. This can break SSH connections with servers using older versions of
 # openssh. Please make sure you understand the implication of different settings
 ssh_config:
+  Hosts:
+    '*':
       StrictHostKeyChecking: no
       ForwardAgent: no
       ForwardX11: no