Add multi site probing and mail notifications

+ Include support for multi site probing (see README for more info)
+ Include support for mail notifications

README.md

@@ -3,4 +3,40 @@ route53-failover
 
 Shell scripts to implement server failover using Amazon Route53, for more information visit:
 
-http://blog.ebrandi.eti.br/2012/11/como-implementar-um-traffic-manager-com-funcionalidade-de-failover-baseado-no-amazon-route53/
+http://blog.ebrandi.eti.br/2012/11/como-implementar-um-traffic-manager-com-funcionalidade-de-failover-baseado-no-amazon-route53/
+
+
+**********************
+Additional information
+**********************
+
+I) Multi-site probing
+
+This script supports two different probing methods: single site and multi site.
+You should use the multi site option on mission critical DNS zones related to a URL where
+maximum uptime and availability are absolutely required.
+
+In order to use the multi site method you must choose 3 different servers:
+one will be the master node, responsible for doing webserver probes and updating the
+Route53 API whenever a host goes down.
+The other two nodes will act as slave nodes: they'll check your hosts and
+send their result back to the master node.
+
+The master node will update your DNS zone if (and only if) any given host
+is reported "down" or "up" from at least 2 different locations (out of 3).
+
+How to configure: set "multisiteprobe" to "1" on all three locations,
+set "probeonly" to "0" on the master node and on the slave nodes set 
+"probeonly" to "1".
+
+On the master node set a friendly name for each slave node using "remoteprobe[1-2]"
+For instante, give each slave node the name of the hosting company where each
+server is located.
+
+Then set "remoteprobefile[1-2]" pointing to the "proberesult" file on each node.
+You may use a SCP url such as scp://username@my.server.com:/home/route53-failover/probe/proberesult
+A HTTP url or UNIX path are also accepted (useful for NFS exports between servers)
+
+Please note that each "proberesult" file has a timestamp and the master node
+requires that these files have been generated less than 5 minutes in the past.
+