DOC: suppress warning + fix reshape example

https://github.com/pydata/pandas/commit/bc610104f96699ff73ce507e79b8be070f126454 defined new `index`, but the previous was still used in later example, and suppress SettingWIthCopyWarning from https://github.com/pydata/pandas/commit/70a17da4003af0b1882deb5bcb28e188335fb9dd