meta: docs badge

Author: jtobin

README.md

@@ -2,6 +2,7 @@
 
 [![](https://img.shields.io/hackage/v/ppad-sha512?color=blue)](https://hackage.haskell.org/package/ppad-sha512)
 ![](https://img.shields.io/badge/license-MIT-brightgreen)
+[![](https://img.shields.io/badge/haddock-sha512-lightblue)](https://docs.ppad.tech/sha512)
 
 A pure Haskell implementation of SHA-512 and HMAC-SHA512 on strict and
 lazy ByteStrings, as specified by RFC's [6234][r6234] and [2104][r2104].