Change service discovery example to use consul/etcd

Author: mad01

README.md

@@ -729,7 +729,10 @@ Pinterest, for example, could have the following microservices: user profile, fo
 
 ### Service Discovery
 
-Systems such as [Zookeeper](http://www.slideshare.net/sauravhaloi/introduction-to-apache-zookeeper) can help services find each other by keeping track of registered names, addresses, ports, etc.
+Systems such as [Consul](https://www.consul.io/docs/index.html) and [Etcd](https://coreos.com/etcd/docs/latest) are among the newer commonly used pull based service discovery solutions today. They solve service registration/de registration of what name, address and port the service is available at. Health checks are often done using a http endpoint. Both Consul and Etcd also have a built in key/value store that can be useful for storing config values or other shared key/values for running a service
+
+Systems such as [Zookeeper](http://www.slideshare.net/sauravhaloi/introduction-to-apache-zookeeper) is a possible older system that can be used as a service discovery service. Zookeeper has commonly been used for master election since it isn't a AP
+ 
 
 ### Disadvantage(s): application layer