Add materials for functional programming update

[martin-martin]

Where to put new files:

• New files should go into a top-level subfolder, named after the article slug. For example: my-awesome-article

How to merge your changes:

1. Make sure the CI code style tests all pass (+ run the automatic code formatter if necessary).
2. Find an RP Team member on Slack and ask them to review & approve your PR.
3. Once the PR has one positive ("approved") review, GitHub lets you merge the PR.
4. 🎉

[martin-martin]

ah, sorry for the commit name, I thought I had done one before adding those flags, but now it's all in one :P

I've just added the code examples, split them into separate files, and added comments to make it somewhat useful. Was maybe more work than it's worth, considering that this isn't super useful material anyway 🤔

Maybe we should eventually replace it with some actually useful examples that go beyond these toy code snippets.

But maybe also ok now, so that we have a materials opt in we can add. LMK.