Add Cosmos: Local block explorer for Starknet

Hey, I have built Cosmos: A lightweight Starknet block explorer designed for local development with starknet-devnet.  It is the only open source block explorer for Starknet. You can check it out here: https://github.com/justmert/cosmos

Can we please add it to the docs, so that developers can run it alongside the devnet to see their blocks, transactions, events, and messages in real-time. Thanks.

