Nixify the hello-world project

[kayvank]

My development machine is nixos. To make the project buildable/runable I nixified the project. This was a straightforward procedure.

Ask: Are you interested in PR to nixify the project? The scope of change will be adding three files:

• flake.nix
• flake.lock
• rust-toolchain.toml And modifying the README for the nix related instruction

[kayvank]

This work is completed in my branch, as it was required to run the demo on my machine. Here is my branch

[kayvank]

PR #86 is for this issue