Document how sort_by() can sort by multiple keys, including an example.

[jbrains]

Fixes #2467

[wader]

LGTM 👍

[itchyny]

The input value can be improved by flipping the foo:3 elements to make it clear the program sorts by bar (program sort_by(.foo) yields the same output currently).

[php-coder]

BTW, it would also be great to have another complicated example where the keys have transformations. For example:

$ echo '[{"foo":"20", "bar":10}, {"foo":"3", "bar":100}, {"foo":"2", "bar":1}, {"foo":"3", "bar":200}]' | jq '. | sort_by([.foo | tonumber], .bar)'
[
  {
    "foo": "2",
    "bar": 1
  },
  {
    "foo": "3",
    "bar": 100
  },
  {
    "foo": "3",
    "bar": 200
  },
  {
    "foo": "20",
    "bar": 10
  }
]

[itchyny]

@php-coder I think such a complicated example with filter combination can be listed in the Cookbook, and actually there is an example using sort_by with tonumber. You can freely edit the wiki page if this example is not enough. BTW I think there should be an example for version sorting. Thanks.

[pkoppstein]

@jbrains - Since #1527 has been closed, could you please add a sentence to the effect that the sort functions are stable. E.g.

As of jq 1.6, the sorting functions are stable.
This means that one way to sort by multiple
criteria is to create a suitable pipeline.

Thanks.