docs(readme): add safe network to notable users

Pull-Request: #4264.

README.md

@@ -98,6 +98,7 @@ used and maintained by [Actyx](https://www.actyx.com).
 - [Locutus](https://github.com/freenet/locutus) - Global, observable, decentralized key-value store.
 - [OpenMina](https://github.com/openmina/openmina) - In-browser Mina Rust implementation.
 - [rust-ipfs](https://github.com/rs-ipfs/rust-ipfs) - IPFS implementation in Rust.
+- [Safe Network](https://github.com/maidsafe/safe_network) - Safe Network implementation in Rust.
 - [Starcoin](https://github.com/starcoinorg/starcoin) - A smart contract blockchain network that scales by layering.
 - [Subspace](https://github.com/subspace/subspace) - Subspace Network reference implementation
 - [Substrate](https://github.com/paritytech/substrate) - Framework for blockchain innovation,