Contributing: Added steps to install rust and cargo

[RyanPaulGannon]

Contributor checklist

• This pull request is on a separate branch and not the main branch

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Description

Updated the CONTRIBUTING.md to help first time contributors correctly download and install rust and cargo on their machines so they can run the application for testing purposes.

Related issue

N/A

[github-actions]

Thank you for the pull request!

The Scribe team will do our best to address your contribution as soon as we can. The following is a checklist for maintainers to make sure this process goes as well as possible. Feel free to address the points below yourself in further commits if you realize that actions are needed :)

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Maintainer checklist

• The CHANGELOG has been updated with a description of the changes for the upcoming release and the corresponding issue (if necessary)

[andrewtavis]

Thanks for getting to this so quickly, @RyanPaulGannon! Great to have this expanded for future contributors :)