RUF017 Autofix uses iadd but docs recommend iconcat

[nicodemus26]

I could not find a substantive difference between iadd and iconcat in cpython aside from some narrower type contexts for iconcat. As the autofix uses iadd to resolve RUF017, I'd suggest updating the documents to match that behavior. If there is a significant difference, it would be helpful to call it out in the docs.

It may be helpful to mention the performance characteristics of the alternatives suggested, as observed here: #9045 (comment)