Add some documentation for SSH pillar.

Signed-off-by: Maximilian Wilhelm <max@rfc2324.org>

zz_EXAMPLE_PILLAR/ssh.sls

@@ -1,5 +1,34 @@
 ssh:
   keys:
+#
+#   <user ID>:
+#     pubkeys:
+#       - "<ssh public key string>"
+#       - "<optional 2nd public key>"
+#     access:
+#
+# Option 1: Access for <username> on all nodes
+#
+#       <username>: global
+#
+# Option 2: Access for <username> on list of given nodes:
+#
+#       <username>:
+#         nodes:
+#           - node1.in.ffho.net
+#           - node2.in.ffho.net
+#
+# Option 3: Access as <username> on all nodes matching at least one of tht
+#           given roles:
+#
+#        <username>:
+#          roles:
+#            - webserver
+#            - router
+#
+#
+# Examples:
+#
     max:
       pubkeys:
         - "ssh-rsa ABC max@pandora"