Fix typo in README.md for 'functions'

[Adlanehichembr]

Proposed change

Type of change

• Example (a notebook demonstrating how to use ZOSPy for a specific application)
• Bugfix (non-breaking change which fixes an issue)
• New analysis (a wrapper around an OpticStudio analysis)
• New feature (other than an analysis)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests
• Documentation (improvement of either the docstrings or the documentation website)

Additional information

• OpticStudio version: ...

Related issues

Checklist

• I have followed the contribution guidelines
• The code has been linted, formatted and tested (see the contribution guidelines).
• Local tests pass. Please fix any problems before opening a PR. If this is not possible, specify what doesn't work and why you can't fix it.
• I tested ZOSPy for all supported Python versions (hatch test -a).
• I added new tests for any features contributed, or updated existing tests.
• I updated CHANGELOG.md with my changes (except for refactorings and changes in the documentation).

If you updated an example:

• I executed all examples and verified that they run without errors (hatch run all-examples).

If you contributed an example:

• I contributed my example as a Jupyter notebook.

[Copilot]

Pull request overview

This PR fixes a spelling error in the README.md file where "fucntions" was misspelled and has been corrected to "functions".

Key Changes

• Corrected spelling of "functions" in the README.md introduction section

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Was approved by accident

[jwmbeenakker]

Thank you for spotting this typo. Out of curiosity, what kind of optical simulations do you aim to do with ZOSPy?