feat: add index_fold examples

[khalidbelk]

Hey : ) Looking through the list module docs yesterday I noticed that index_fold had a pretty vague example (the {...} placeholder). The function signature is clear, and probably enough for a lot of people, but it kinda lacks information about why, in practice, we would want to use the index parameter.

This adds 2 small examples (with lists of two different data types: strings and integers) that should be intuitive enough to understand the use case of index_fold.

[lpil]

I could be wrong as I'm on my phone, but it looks like that line is quite long. Could you wrap the line longs the way the formatter would please 🙏

[khalidbelk]

Yes indeed, done ;)

[lpil]

Lovely!! Thank you, this is much better with proper examples.