link maintenance

[keewis]

This fixes a few broken links in our RST files and moves a few links.

Note that the module referenced here:

xarray/doc/internals/how-to-add-new-backend.rst

Lines 430 to 432 in b5a84ba

	If you support more complex indexing as `explicit indexing` or
	`numpy indexing`, you can have a look to the implemetation of Zarr backend and Scipy backend,
	currently available in :py:mod:`~xarray.backends` module.

does not have a API page, yet. Should we try to fix that, or would linking to github be better? Also, were the explicit indexing and numpy indexing meant to be links or literal text?

• Passes pre-commit run --all-files

[max-sixty]

Thanks @keewis !

[dcherian]

Thanks @keewis

[keewis]

thanks for the reviews, @max-sixty, @dcherian