Fix and improve "rrset-order" documentation

• The section about the "none" order says: "When no ordering is specified, this is the default." This is rather inaccurate: "none" is only the default if there are explicit "rrset-order" rules specified in the configuration file and none of them matches the query (see also below for notes about the implicit default).

• The explanation of the sample configuration claims that a rule with "name host.example.com" matches queries "that have host.example.com as a suffix". As already mentioned above, this is not true - the relevant "rrset-order" rule only affects host.example.com, not any of its subdomains.

• The last paragraph says: "By default, records are returned in random order." This is only true if there are no explicit "rrset-order" rules configured. In other words, "rrset-order { order random; }" is present in bin/named/config.c, so it is the implicit default, but if there are explicit "rrset-order" rules present in named.conf, they override the implicit default

Also I would be useful to document the different behaviour of names which include wildcards and those that do not.