Update README.md (#8132)

Doc-change that would have avoided my mistake that I made a bug-report about.

mockwebserver/README.md

@@ -114,7 +114,7 @@ assertEquals("{}", request.getBody().readUtf8());
 #### Dispatcher
 
 By default MockWebServer uses a queue to specify a series of responses. Use a
-Dispatcher to handle requests using another policy. One natural policy is to
+Dispatcher (`import okhttp3.mockwebserver.Dispatcher`) to handle requests using another policy. One natural policy is to
 dispatch on the request path.
 You can, for example, filter the request instead of using `server.enqueue()`.