Service Discovery: add license tags

- ref. https://github.com/awesome-foss/awesome-sysadmin/issues/416

README.md

@@ -633,9 +633,9 @@ _Related: [Databases](#databases), [Monitoring](#monitoring)_
 
 *[Service discovery](https://en.wikipedia.org/wiki/Service_discovery) is the process of automatically detecting devices and services on a computer network.*
 
-- [Consul](https://www.consul.io/) - Consul is a tool for service discovery, monitoring and configuration. ([Source Code](https://github.com/hashicorp/consul))
-- [etcd](https://etcd.io/) - distributed K/V-Store, authenticating via SSL PKI and a REST HTTP Api for shared configuration and service discovery. ([Source Code](https://github.com/coreos/etcd))
-- [ZooKeeper](http://zookeeper.apache.org/) - ZooKeeper is a centralized service for maintaining configuration information, naming, providing distributed synchronization, and providing group services. ([Source Code](https://github.com/apache/zookeeper))
+- [Consul](https://www.consul.io/) - Consul is a tool for service discovery, monitoring and configuration. ([Source Code](https://github.com/hashicorp/consul)) `MPL-2.0`
+- [etcd](https://etcd.io/) - distributed K/V-Store, authenticating via SSL PKI and a REST HTTP Api for shared configuration and service discovery. ([Source Code](https://github.com/coreos/etcd)) `Apache-2.0`
+- [ZooKeeper](http://zookeeper.apache.org/) - ZooKeeper is a centralized service for maintaining configuration information, naming, providing distributed synchronization, and providing group services. ([Source Code](https://github.com/apache/zookeeper)) `Apache-2.0`
 
 
 ### Software Containers