[FAB-14429] Add Raft to intro doc

Cherry picked from merged master

Change-Id: Icc0efd15b3aa6d1c98c52f095ef647629b69916d
Signed-off-by: joe-alewine <Joe.Alewine@ibm.com>
(cherry picked from commit 3662466de63d79f34051bc2bfe6ba03f5e440bc7)

docs/source/whatis.md

@@ -290,11 +290,11 @@ particular deployment or solution. This modular architecture allows the platform
 to rely on well-established toolkits for CFT (crash fault-tolerant) or BFT
 (byzantine fault-tolerant) ordering.
 
-In the currently available releases, Fabric offers a CFT ordering service
-implemented with [Kafka](https://kafka.apache.org/) and
-[Zookeeper](https://zookeeper.apache.org/). In subsequent releases, Fabric will
-deliver a [Raft consensus ordering service](https://raft.github.io/) implemented
-with etcd/Raft and a fully decentralized BFT ordering service.
+Fabric currently offers two CFT ordering service implementations. The first is
+based on the [`etcd` library](https://coreos.com/etcd/) of the [Raft protocol](https://raft.github.io/raft.pdf).
+The other is [Kafka](https://kafka.apache.org/) (which uses [Zookeeper](https://zookeeper.apache.org/)
+internally). For information about currently available ordering services, check
+out our [conceptual documentation about ordering](../orderer/ordering_service.html).
 
 Note also that these are not mutually exclusive. A Fabric network can have
 multiple ordering services supporting different applications or application