add keccak-chain link to examples_projects.md

src/examples_projects.md

@@ -3,3 +3,4 @@
 > This section contains examples and projects that use Sonobe. You can find isolated examples too in the dir [sonobe/examples](https://github.com/privacy-scaling-explorations/sonobe/tree/main/examples).
 
 - [https://github.com/dmpierre/sonobe-btc](https://github.com/dmpierre/sonobe-btc): implementation of an on-chain Bitcoin light client leveraging Sonobe: uses nova to verify bitcoin's proof of work over 100k blocks and groth16 to land the zkSNARK IVC proof on chain.
+- [keccak-chain-sonobe](https://github.com/arnaucube/keccak-chain-sonobe): example using Sonobe & Circom circuits, proving a chain of Keccak256 hashes.