[Doc] Update <ReferenceManyInput> documentation to mention it cannot reorder its items

[djhi]

Problem

• <ReferenceManyInput> documentation examples don't explain you have to set the disableReordering prop on <SimpleFormIterator>
• <ReferenceManyInput> documentation does not mention the reordering limitation

Solution

Update <ReferenceManyInput> documentation to mention it cannot reorder its items and improve the examples.

Additional Checks

• The PR targets master for a bugfix, or next for a feature
• The documentation is up to date

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