document where to find the default whitelist, fixes schweikert#75

Author: schweikert

README.md

@@ -8,7 +8,10 @@
 - Homepage = http://postgrey.schweikert.ch/
 - Project + Issues = https://github.com/schweikert/postgrey
 
-## Requirements
+## Installation
+
+It is recommended that you use Postgrey from your Linux distribution, if
+possible. Otherwise, you will need to install first the following requirements:
 
 - Perl >= 5.6.0
 - Net::Server (Perl Module)
@@ -18,16 +21,24 @@
 - Digest::SHA (Perl Module, only for --privacy option)
 - NetAddr::IP
 
+## Documentation
 
-## Dev Documentation
-
-To see POD documentation in postgrey. Execute:
+To see the documentation in postgrey. Execute:
 ```bash
 perldoc postgrey
 ```
 
-    
+(or `man postgrey` if you are using a pre-built Postgrey distribution).
+
+## Updating the whitelist
+
+You can find at the following URL the latest whitelist that is included
+in the Postgrey distribution:
+
+<https://postgrey.schweikert.ch/pub/postgrey_whitelist_clients>
 
+If you fetch this list automatically, please make sure that you don't do it too
+frequently (updating once a day is ok).
 
 ## Mailing-List and getting Help
 

postgrey

@@ -957,6 +957,16 @@ anything that matches C<regexp> (the full address is matched).
 
 =back
 
+=head2 Updating the postgrey default whitelist
+
+You can find at the following URL the latest whitelist that is included
+in the Postgrey distribution:
+
+L<https://postgrey.schweikert.ch/pub/postgrey_whitelist_clients>
+
+If you fetch this list automatically, please make sure that you don't do it too
+frequently (updating once a day is ok).
+
 =head2 Auto-whitelisting clients
 
 With the option --auto-whitelist-clients a client IP address will be