Flesh out README

README.md

 # go-httpbin
 
-A WIP golang port of https://httpbin.org/.
+A reasonably complete and well-tested golang port of [Kenneth Reitz][kr]'s
+[httpbin][httpbin-org] service, with zero dependencies outside the go stdlib.
 
 [![GoDoc](https://godoc.org/github.com/mccutchen/go-httpbin?status.svg)](https://godoc.org/github.com/mccutchen/go-httpbin)
 [![Build Status](https://travis-ci.org/mccutchen/go-httpbin.svg?branch=master)](http://travis-ci.org/mccutchen/go-httpbin)
 [![Coverage](http://gocover.io/_badge/github.com/mccutchen/go-httpbin/httpbin?0)](http://gocover.io/github.com/mccutchen/go-httpbin/httpbin)
 
-## Building
+## Usage
+
+Run as a standalone binary, configured by command line flags or environment
+variables:
+
+```
+$ go-httpbin -help
+Usage of ./dist/go-httpbin:
+  -listen string
+        Listen address (default ":8080")
+  -max-duration duration
+        Maximum duration a response may take (default 10s)
+  -max-memory int
+        Maximum size of request or response, in bytes (default 1048576)
+```
+
+## Installation
+
+```
+go get github.com/mccutchen/go-httpbin/...
+```
+
+## See also
+
+ - [kennethreitz/httpbin][httpbin-repo] — the original Python version, without
+   which this knock-off wouldn't exist
+ - [ahmetb/go-httpbin][ahmet-go-httpbin] — another golang port
+
+## Development
+
+### Building
 
 ```
 make
 ```
 
-## Testing
+### Testing
 
 ```
 make test
 make testcover
 ```
 
-## Running
+### Running
 
 ```
 make run
 ```
+
+[kr]: https://github.com/kennethreitz
+[httpbin-org]: https://httpbin.org/
+[httpbin-repo]: https://github.com/kennethreitz/httpbin
+[ahmet-go-httpbin]: https://github.com/ahmetb/go-httpbin