DOC: tril_indices triu_indices order

[benjamin-lieser]

Issue with current documentation:

The order of indices in not specified which makes it hard to rely on.

Idea or request for content:

Document the current behavior and make it part of the function contract:

"The indices returned are sorted first with respect to the row and then the column"

[ajayjanapareddi]

Hi,
Although it may be obvious, I think updating the docs seems like a valid suggestion for this. I will raise a PR shortly.