fix typo

README.md

@@ -286,7 +286,7 @@ message, as specified in our interface definition.
 
 #### Server implementation
 
-[HelloWorldServer.java](https://github.com/grpc/grpc-java/blob/master/examples/src/main/java/io/grpc/examples/HelloWorldServer.java)
+[HelloWorldServer.java](https://github.com/grpc/grpc-java/blob/master/examples/src/main/java/io/grpc/examples/helloworld/HelloWorldServer.java)
 shows the other main feature required to provide a gRPC service; making the service
 implementation available from the network.
 
@@ -324,7 +324,7 @@ how all this works in a bit more detail in our language-specific documentation.
 Client-side gRPC is pretty simple. In this step, we'll use the generated code
 to write a simple client that can access the `Greeter` server we created
 in the [previous section](#server). You can see the complete client code in
-[HelloWorldClient.java](https://github.com/grpc/grpc-java/blob/master/examples/src/main/java/io/grpc/examples/HelloWorldClient.java).
+[HelloWorldClient.java](https://github.com/grpc/grpc-java/blob/master/examples/src/main/java/io/grpc/examples/helloworld/HelloWorldClient.java).
 
 Again, we're not going to go into much detail about how to implement a client;
 we'll leave that for the tutorial.