Update Options.md

[burnchar]

Updated options to reflect current source code (probably not complete)

Please remove the pasted code that I forgot to remove:

///

/// The format string used when writing DateTime values, or DateOnly values on supported frameworks, that have a time component. The default is "O".
///

public string? DateOnlyFormat { get; set; }

///

/// The format string used when writing TimeOnly values.
///

public string? TimeOnlyFormat { get; set; }