DOC: Clarify loc and iloc functionality in user_guide/indexing.html

[bluestarunderscore]

• Addresses DOC: iloc boolean indexing potential wording error #47224

This PR fixes the incorrect description of iloc and adds a brief comparison to loc to make the warning more clear:

"While loc supports two kinds of boolean indexing, iloc only supports indexing with a boolean array."

[mroeschke]

Suggested change

	While ``loc`` supports two kinds of boolean indexing, ``iloc`` only supports indexing with a
	boolean array. If the indexer is a boolean ``Series``, an error will be raised. For instance,
	in the following example, ``df.iloc[s.values, 1]`` is ok. The boolean indexer is an array.
	But ``df.iloc[s, 1]`` would raise ``ValueError``.
	While ``loc`` supports two kinds of boolean indexing, ``iloc`` only supports indexing with a
	boolean array. If the indexer is a boolean ``Series``, an error will be raised. For instance,
	in the following example, ``df.iloc[s.values, 1]`` is ok. The boolean indexer is an array.
	But ``df.iloc[s, 1]`` would raise ``ValueError``.