Some more documentation.

README.rst

@@ -54,6 +54,11 @@ Then the line will be::
 
     @cert-authority *.example.com ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQC2fAkeidfnPn712B4uW3XhKyFt9FcJtVwSPKDSCykULg3X5gVV/Xa1yb4ameY3ihXOqQOlG3YpYnOQ8KdM67WtnERVbTJIfieRjGzoURz9NquLFXSKsuQrXMWRNHqXAHw7VirPvKL4cSc4l00Az1HDnHhMIclPY8G+8SkRIRsTwwwa5QjGF2wuhC6j5UHJSaF7qLFw9FSaCsEJTkQxtCD4+Rd/dxv3kVWSkm5DbNG0z3QHyISW7XDvyXP+1ccSb5+IWC0yQCT4OJNFUMDb+SdD7AzDHfI9Z5zTp56uGV23lywWhSvv20UPA0SyXJNGPOw7uJ1ak8q4SBh60PtOENQf ssh-ca
 
+#. You can also add it system wide by adding the above line to
+`/etc/ssh/ssh_known_hosts` and the following line to your `ssh_config` file::
+
+    GlobalKnownHostsFile /etc/ssh/ssh_known_hosts
+
 #. For strict security, add the following line to you `ssh_config` file::
 
     StrictHostKeyChecking yes