🦀 Rust compiler now required to install terra from source

[javabster]

🚨 Announcement! 🚨

With the merging of #7658 contributors to Qiskit will now need to have a Rust compiler installed in order to install Qiskit Terra from source.

To update your dev environment you can check out the updated Contributing Guidelines or follow the instructions in the rust documentation on how to install the compiler.

Note: don't forget you may need to restart your shell or update your current session according to the rust docs:

To get started you may need to restart your current shell. 
This would reload your PATH environment variable to include Cargo's bin directory ($HOME/.cargo/bin).

To configure your current shell, run: source $HOME/.cargo/env

[jwoehr]

On Ubuntu(-like) Linux distros, install Rust via apt install cargo