Reducer example on Newcomer Examples

[samwightt]

I added a simple reducer example on a fork of the docs here. Would y'all be open to me making a pull request to add it to the docs?

[ryyppy]

Uff, well these kind of cheatsheets tend to get really unwieldy as soon as you mash up too many topics.

We'd probably need to think about a proper independent "Guides" section with a bunch of tutorials and more thorough resources?