Add resource: Calculator Campus

[nmajor]

Resources

• Link: https://www.calculatorcampus.com/
  Why it helps students: It provides free practical calculators with formulas, examples, and named sources.

Checklist

• Each entry added in the correct section, in alphabetical order (case-insensitive)
• Each entry follows the format from CONTRIBUTING.md: - **[Name](https://homepage)** - Short description.
• Each entry meets the Quality Standards: real, maintained, reputable, pricing noted
• No entry duplicates an existing one in the same section

[github-actions]

Thanks for your first PR! A couple of things that'll speed up review: place your entry in its correct alphabetical position, and make sure it meets the Quality Standards (real, maintained, reputable, with pricing noted). CI will check the entry format and alphabetical order automatically, see CONTRIBUTING.md for the full checklist.

[yakew7]

Hey @nmajor! Will check your pr and merge it if it is good meanwhile could you pls star the repo since it helps the project grow and also helps others find this project