README file for sqlgrey updated content

Don't touch these files, they are automatically updated when
you run update_sqlgrey_config:
- clients_fqdn_whitelist: don't greylist these DNS names [*]
- clients_ip_whitelist  : don't greylist these IP addresses [*]
- dyn_fqdn.regexp       : used by new 'smart' algorithm [x]
- smtp_server.regexp    : used by new 'smart' algortihm [x]

[*]: in use starting with 1.4.0
[x]: in use since 1.5.1, regexps looking for known fqdns patterns
