Add a deployment guide

[anurag]

This PR adds a deployment guide in response to #171.

[ghost]

I don't think the guide should serve as an advertisement platform for deployment services.

The guide should be neutral, and explain a basic deployment with optional TLS and specificities for Linux / Windows / MacOS. All of that is missing, except the explicit parts for Render, which IMO are a niche use-case.

Render should have the guide on deploying Rocket applications, not the other way around.

[jebrosen]

I am opposed to including in the guide any content dependent on a specific deployment service, except in the presence of a prenegotiated agreement. I think linking to tutorials for several platforms or services would be okay, as long as it does not look like an endorsement of any particular platform over any other.

I would be okay with including generic examples of creating docker or other containers, uploading binaries to an external server and configuring startup with an initscript or systemd service, and so on. I would also be fine with including a section along the lines of "platforms that respect rust-toolchain files, such as Render, this or that heroku buildpack, or QuuxBar".

[anurag]

Makes sense. We already have a deployment guide for Rust at https://render.com/docs/deploy-rocket-rust, and we're happy to contribute a guide with standard examples that don't rely on Render.