Add Haskell implementation by @zenhack.

doc/otherlang.md

@@ -26,6 +26,7 @@ project's documentation for details.
 * [C](https://github.com/opensourcerouting/c-capnproto) by [OpenSourceRouting](https://www.opensourcerouting.org/) / [@eqvinox](https://github.com/eqvinox) (originally by [@jmckaskill](https://github.com/jmckaskill))
 * [D](https://github.com/capnproto/capnproto-dlang) by [@ThomasBrixLarsen](https://github.com/ThomasBrixLarsen)
 * [Go](https://github.com/glycerine/go-capnproto) by [@glycerine](https://github.com/glycerine) (originally by [@jmckaskill](https://github.com/jmckaskill))
+* [Haskell](https://github.com/zenhack/haskell-capnp) by [@zenhack](https://github.com/zenhack)
 * [Java](https://github.com/capnproto/capnproto-java/) by [@dwrensha](https://github.com/dwrensha)
 * [Javascript](https://github.com/capnp-js/capnp-js-base) by [@popham](https://github.com/popham)
 * [Javascript](https://github.com/jscheid/capnproto-js) (older, abandoned) by [@jscheid](https://github.com/jscheid)