readme: add benchmarks

Signed-off-by: Ignacio Hagopian <jsign.uy@gmail.com>

README.md

@@ -9,13 +9,30 @@ This implementation is currently targeting BN254 scalar field (i.e: BabyJubJub b
 - [go-iden3-crypto](https://github.com/iden3/go-iden3-crypto/tree/master/poseidon) implementation.
 - [poseidon-rs](https://github.com/arnaucube/poseidon-rs) implementation.
 
+See the [compatibility tests](https://github.com/jsign/poseidon/blob/main/src/bn254/tests.zig).
+
 The parameters for BN254 were [pulled from CircomLib](https://github.com/iden3/circomlibjs/blob/4f094c5be05c1f0210924a3ab204d8fd8da69f49/src/poseidon_constants.json) which can be generated with the [official Sage script](https://extgit.iaik.tugraz.at/krypto/hadeshash) and transformed using a [CircomLibJS tool](https://github.com/iden3/circomlibjs/blob/main/tools/poseidon_optimize_constants.js) created by @jbaylina.
 
 Supporting other fields (e.g: BLS12-381 scalar field) would only involve generating the parameters.
 
 ## Benchmarks
 
-To be included soon.
+This implementation doesn't use assembly (e.g: AVX2) or SIMD instructions for finite field operations.
+
+Run on _AMD Ryzen 7 3800XT_:
+```
+$ zig build run -Doptimize=ReleaseFast 
+Poseidon(width=1) took 13µs
+Poseidon(width=2) took 20µs
+Poseidon(width=3) took 26µs
+Poseidon(width=4) took 35µs
+Poseidon(width=5) took 44µs
+Poseidon(width=6) took 55µs
+Poseidon(width=7) took 64µs
+Poseidon(width=8) took 73µs
+Poseidon(width=9) took 81µs
+Poseidon(width=10) took 97µs
+```
 
 ## Future work