Standardize ISO method name in README and docs

[froschdesign]

Updated the method name from createIteratorFromIso3166 to createIteratorFromISO3166 in README.md and docs/index.md. This standardizes the capitalization in the method name, ensuring consistency throughout the documentation.

holidayChecker/src/HolidayIteratorFactory.php

Lines 77 to 84 in f7fbe36

	/**
	* Create a HolidayIterator from an ISO 3166-code.
	*
	* @param string $isoCode
	*
	* @return HolidayIterator
	*/
	public function createIteratorFromISO3166(string $isoCode): HolidayIterator

[heiglandreas]

Thank you for taking the time to create this PR!

But to be honest: In in the light of the recently accepted RFC on Casing of acronyms in class and method names that states that "Abbreviations, acronyms, and initialisms should be treated like regular words, thus they should be written with an uppercase first character, followed by lowercase characters" I'd rather say that the casing of the function name was wrong in the first place 🙈

That should have been createIteratorFromIso3166 all along!

THanks for making me aware of that. If you want to change that PR I'd be more than happy, otherwise I'd do that change later.