Add a link to the latest Gimli specification

README.md

@@ -8,7 +8,7 @@ The Hydrogen library is a small, easy-to-use, hard-to-misuse cryptographic libra
 
 Features:
 - Consistent high-level API, inspired by libsodium. Instead of low-level primitives, it exposes simple functions to solve common problems that cryptography can solve.
-- 100% built using just two cryptographic building blocks: the [Curve25519](https://cr.yp.to/ecdh.html) elliptic curve, and the [Gimli](https://gimli.cr.yp.to/) permutation.
+- 100% built using just two cryptographic building blocks: the [Curve25519](https://cr.yp.to/ecdh.html) elliptic curve, and the [Gimli](https://csrc.nist.gov/CSRC/media/Projects/Lightweight-Cryptography/documents/round-1/spec-doc/gimli-spec.pdf) permutation.
 - Small and easy to audit. Implemented as one tiny file for every set of operation, and adding a single `.c` file to your project is all it takes to use libhydrogen in your project.
 - The whole code is released under a single, very liberal license (ISC).
 - Zero dynamic memory allocations and low stack requirements (median: 32 bytes, max: 128 bytes). This makes it usable in constrained environments such as microcontrollers.