Add deployment guide for builders

The builder docs cover local development well (build, MockChain testing, local node validation) but there is no guide for deploying contracts to testnet. External developers are hitting a wall once they get past building and testing and want to deploy.

We should add a deployment guide in `docs/builder/guides/deployment.md` covering how to create accounts and faucets on testnet via the miden-client, deploy and initialize contracts, and verify the deployment.

The guide should be created at docs/builder/guides/deployment.md. Start by reviewing existing builder docs to understand the structure and tone. Research how to create accounts and faucets on testnet using the miden-client, and the steps to deploy and initialize contracts. Verify the deployment process works by testing it locally or on testnet.

Rédigé par le modèle d'indexation à partir du texte de l'issue.