Improve CONTRIBUTING.md with clear installation instructions and detailed development process

[teddyCodex]

Description

This PR updates the CONTRIBUTING.md documentation to provide clearer instructions for setting up a development environment and contributing to the project. Key changes include:

• Added detailed steps to install and load the usethis, devtools, and lintr packages.
• Improved the formatting of the pull request process, making it easier to understand for new contributors.
• Updated various sections for better readability and clarity.

What kind of change(s) are included?

• [ ] Feature (adds or updates new capabilities)
• [ ] Bug fix (fixes an issue).
• [x] Enhancement (adds functionality, improves documentation).
• [ ] Breaking change (these changes would cause existing functionality to not work as expected).

Checklist

Please ensure that all boxes are checked before indicating that this pull request is ready for review.

• [x] I have read and followed the CONTRIBUTING.md guidelines.
• [x] I have searched for existing content to ensure this is not a duplicate.
• [x] I have performed a self-review of these additions (including spelling, grammar, and related).
• [x] I have added comments to my code to help provide understanding.
• [x] I have added a test which covers the code changes found within this PR.
• [x] I have deleted all non-relevant text in this pull request template.
• [x] Reviewer assignment: Tag a relevant team member to review and approve the changes.

[teddyCodex]

@the-mayer file updated.

Side note: Did not find a NEWS.md file in the repo. Commented out the line referencing it:

For user-facing changes, add a bullet to the top of NEWS.md (i.e. just below the first header). Follow the style described in https://style.tidyverse.org/news.html.

Suggest restoring this line when the file exists to avoid any confusion