DOC: Update docstring for Index.from_variables()

[VeckoTheGecko]

There was no mention of the options keyword

• Closes None

Docstring of Dataset.set_xindex for reference:

xarray/xarray/core/dataset.py

Lines 4983 to 5003 in bf8da57

	def set_xindex(
	self,
	coord_names: str | Sequence[Hashable],
	index_cls: type[Index] | None = None,
	**options,
	) -> Self:
	"""Set a new, Xarray-compatible index from one or more existing
	coordinate(s). Existing index(es) on the coord(s) will be replaced.
	Parameters
	----------
	coord_names : str or list
	Name(s) of the coordinate(s) used to build the index.
	If several names are given, their order matters.
	index_cls : subclass of :class:`~xarray.indexes.Index`, optional
	The type of index to create. By default, try setting
	a ``PandasIndex`` if ``len(coord_names) == 1``,
	otherwise a ``PandasMultiIndex``.
	**options
	Options passed to the index constructor.

[VeckoTheGecko]