fix #75 Add Flux.collect exercise in solution branch

[paweusz]

As currently there's no exercise for Flux.collect...() methods I thought that at least one case could be helpful.

[simonbasle]

Hi @paweusz and thanks for offering this contribution.
Mentioning collectList could indeed make sense.

There are 3 parts to adding an operator to the hands on, which cannot be covered by a single PR: master has the empty exercise to be filled by the user, techio_course has the same + a more fleshed out description of the operator and what's expected of the user in a markdown file (displayed along the code on tech.io) and the third branch solution has the filled solution to the exercise.

I think ideally an issue would be a better format, as you can A) discuss the solution and techio_course parts and B) optionally submit 3 PRs that each refer the same issue. wdyt?

[paweusz]

Thx, will do.