directory.default: update pillar.example

New behavior properly explained in pillar.example

Warning: changes directory.default when used with non-standard documentroot.
Now uses documentroot, instead of previously "default" documentroot path.

pillar.example

       SSLCertificateChainFile: /etc/ssl/mycert.chain.pem # if you require a chain of server certificates file
 
       Directory:
-        # "default" is a special case; Adds ``/path/to/www/dir/example.com``
+        # "default" is a special case; uses DocumentRoot value
         # E.g.: /var/www/example.com
         default:
           Options: -Indexes +FollowSymLinks