Add link.

README.md

@@ -683,7 +683,7 @@ Libraries to help manage database schemas and migrations.
 * [Ginq](https://github.com/akanehara/ginq) - Another PHP library based on .NET's LINQ.
 * [JsonMapper](https://github.com/cweiske/jsonmapper) - A library that maps nested JSON structures onto PHP classes.
 * [Knapsack](https://github.com/DusanKasan/Knapsack) - Collection library inspired by Clojure's sequences.
-* [msgpack.php](https://github.com/rybakit/msgpack.php) - A pure PHP implementation of the MessagePack serialization format.
+* [msgpack.php](https://github.com/rybakit/msgpack.php) - A pure PHP implementation of the [MessagePack](https://msgpack.org/) serialization format.
 * [PINQ](https://github.com/TimeToogo/Pinq) - A PHP library based on .NET's LINQ (Language Integrated Query).
 * [Porter](https://github.com/ScriptFUSION/Porter) - Data import abstraction framework.
 * [Serializer](https://github.com/schmittjoh/serializer) - A library for serialising and de-serialising data.