Improvement for `Selection` documentation.

[1uc]

From the documentation it's unclear to me if a libsonata.Selection can be unsorted, or contain duplicate elements. What happens if the arguments to the ctor are unsorted or contain duplicate elements? It would be helpful to make the documentation explicit in this regard. Regarding selection.ranges do I get a copy or just a reference?

"The documentation" refers to:
https://libsonata.readthedocs.io/en/stable/#selection
https://libsonata.readthedocs.io/en/stable/api.html#libsonata.Selection

[mgeplf]

Good points, I will make that more clear.