Updated echo server documentation.

examples/echo/README.md

 Example Echo Client & Server
 ====
 
 This echo client/server demonstrate how to create and use a mojom interface,
 as well as demonstrating one way to communicate between mojo applications.
 
+For more general introduction to Mojo, refer to the [Mojo

[jimbe, 2015/10/30 20:28:29]

s/For more general introduction to Mojo/For a deeper dive into this code/

The issue is that the tutorial is really about writing code, not about learning
Mojo theory.

[Sean Klein, 2015/10/30 22:31:54]

Done.

+Tutorial](https://docs.google.com/document/d/1mufrtxTk8w9qa3jcnlgqsYkWlyhwEpc7aWNaSOks7ug).
+
 ## Running the Echo Client & Server
 
 ```
 $ ./mojo/tools/mojob.py gn
 $ ./mojo/tools/mojob.py build
 $ ./out/Debug/mojo_shell mojo:echo_client
 ```
 You should see output along the lines of:
 
 ```
@@ skipping 151 matching lines @@
 This server creates an `EchoImpl` object when it is constructed, and for each
 call to `Create`, binds the request to this single implementation. A
 `BindingSet` is used so that multiple requests can be bound to the same object.
 
 ### Server 3: OneAtATimeServer
 
 This server creates an `EchoImpl` object, like the `SingletonServer`, but uses a
 single `Binding`, rather than a `BindingSet`. This means that when a new client
 connects to the OneAtATimeServer, the previous binding is closed, and a new
 binding is made between the new client and the interface implementation.
+
+The OneAtATimeServer is an unusual case, as it actually contains a race
+condition for multiple clients. If a new client binds to the server before the

[jimbe, 2015/10/30 20:28:29]

For the first sentence, how about:
The OneAtATimeServer demonstrates a pattern that should usually be avoided
because it contains a race condition for multiple clients.

[Sean Klein, 2015/10/30 22:31:54]

Done.

+first client managed to call EchoString, the first client's call would cause an
+error. Unless you know what you are doing, it is advised to avoid creating a

[jimbe, 2015/10/30 20:28:29]

s/know what you are doing/have a specific use case for this behavior/

[Sean Klein, 2015/10/30 22:31:54]

Done.

+server like this.