[mojo-doc] Add note about in-process messaging

docs/mojo_in_chromium.md

Index: docs/mojo_in_chromium.md
diff --git a/docs/mojo_in_chromium.md b/docs/mojo_in_chromium.md
index 58ab08ea1d877275b790688f7c640cf1e77a490a..9ec5588e4376ea99f84b5d9562aa91348911e521 100644
--- a/docs/mojo_in_chromium.md
+++ b/docs/mojo_in_chromium.md
@@ -181,6 +181,11 @@ request and writes it to one end of the pipe. Eventually (and incidentally,
 very soon after), `impl`'s internal `mojo::Binding` will decode this message and
 dispatch a call to `impl.Frobinate()`.
 
+**NOTE:** In this example the service and client are in the same process, and
+this works just fine. If they were in different processes (see the example below
+in [Exposing Services in Chromium](#Exposing-Services-in-Chromium)), the call
+to `Frobinate()` would look exactly the same!
+
 ### Responding to Requests
 
 A common idiom in Chromium IPC is to keep track of IPC requests with some kind