doc: clarify client concurrency (grpc#3001)

Author: dfawley

Documentation/concurrency.md

@@ -7,8 +7,12 @@ guidelines.
 
 A [ClientConn][client-conn] can safely be accessed concurrently. Using
 [helloworld][helloworld] as an example, one could share the `ClientConn` across
-multiple goroutines to create multiple `GreeterClient` types. In this case, RPCs
-would be sent in parallel.
+multiple goroutines to create multiple `GreeterClient` types. In this case,
+RPCs would be sent in parallel.  `GreeterClient`, generated from the proto
+definitions and wrapping `ClientConn`, is also concurrency safe, and may be
+directly shared in the same way.  Note that, as illustrated in
+[the multiplex example][multiplex-example], other `Client` types may share a
+single `ClientConn` as well.
 
 ## Streams
 
@@ -24,10 +28,12 @@ call `RecvMsg` on the same stream in different goroutines.
 Each RPC handler attached to a registered server will be invoked in its own
 goroutine. For example, [SayHello][say-hello] will be invoked in its own
 goroutine. The same is true for service handlers for streaming RPCs, as seen
-in the route guide example [here][route-guide-stream].
+in the route guide example [here][route-guide-stream].  Similar to clients,
+multiple services can be registered to the same server.
 
 [helloworld]: https://github.com/grpc/grpc-go/blob/master/examples/helloworld/greeter_client/main.go#L43
 [client-conn]: https://godoc.org/google.golang.org/grpc#ClientConn
 [stream]: https://godoc.org/google.golang.org/grpc#Stream
 [say-hello]: https://github.com/grpc/grpc-go/blob/master/examples/helloworld/greeter_server/main.go#L41
 [route-guide-stream]: https://github.com/grpc/grpc-go/blob/master/examples/route_guide/server/server.go#L126
+[multiplex-example]: https://github.com/grpc/grpc-go/tree/master/examples/features/multiplex