Add code for methods tutorial

[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. 🎉

[stephengruppetta]

@martin-martin no comments specific to the materials. Only one comment in the main review may or may not lead to a small change here

[martin-martin]

@stephengruppetta what change were you thinking about? The tuple parentheses?