Collate old QnA's

[miguelraz]

We have a lot of old trainings with a lot of answered questions, as well as rust-experts. We might as well stick them at the bottom of the training materials.

[jonathanpallant]

We should probably think carefully about how to structure them, as a dumping ground of random questions isn't very easy to consume. Where questions highlight matters that aren't covered well in the material, we should update the slides and/or exercises.