reproject_interp missing method description or reference

The docs reproject_interp (https://reproject.readthedocs.io/en/stable/api/reproject.reproject_interp.html#reproject.reproject_interp) are currently missing an explanation of how the method works, or a reference to somewhere else that explains how the method works.

Start with the reproject_interp API documentation at the linked Read the Docs page and inspect the existing method documentation and nearby references. Add an explanation of how the method works or link to an authoritative explanation, then verify that the rendered API page clearly provides this information.

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