Add README to collapsed forwarding code.

code/collapsed-forwarding/README.md

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+# Collapsed Forwarding Example: Request Batcher
+
+This is an example of collapsed forwarding which batches together requests for the same URL. Every five seconds, a `requestBatcher` flushes its batches of requests by handling one request from each batch and giving the same result to the rest of the requests in that batch.
+
+This code was written for the sole purpose of explaining the concept of collapsed forwarding. It is not intended for production use and has known inefficiencies and flaws.
+
+## Getting it running
+
+```bash
+$ go build && ./collapsed-forwarding
+[server] running on port :8081
+[proxy] running on port :8080
+```
+
+Once the proxy and server are running, make a request to `localhost:8080/<URL>`. The response should be the provided <URL>:
+
+```bash
+$ curl localhost:8080/test
+/test
+```
+
+Make several requests to the proxy in the background.
+
+```bash
+$ curl localhost:8080/test &
+$ curl localhost:8080/test &
+$ curl localhost:8080/test &
+$ curl localhost:8080/test &
+```
+
+The application should log each request, find four batched requests, and then make a single request to the server:
+
+```
+[proxy] /test
+[proxy] /test
+[proxy] /test
+[proxy] /test
+4 batched requests under key "/test"
+[server] /test
+```