Add references per reviewer comment

[mdhaber]

Reference issue

https://github.com/openjournals/joss-reviews/issues/5092#issuecomment-1504807777

What does this implement/fix?

@SaranjeetKaur suggested:

@mdhaber - it might be helpful to add link to the references in the section "Statement of need" (that is, for all the 3 questions, when you are sharing examples which were introduced in the Summary)

Also when you are describing the state of the ecosystem before the release of SciPy 1.9.0 and how it was partially met by tutorials, blog posts, medium.com, and niche packages - share some references here too, if possible.

This PR attempts to address these comments.

[SaranjeetKaur]

This is all good @mdhaber!