Restore missing K-Means CSV files. Slight changes to example text.

[lindapaiste]

Fixes #1341.

I restored the deleted files to the kmeans folder while keeping the copies in the dbscan folder, which means that we have essentially the same files in two places. I'm not sure if this is the right approach. It keeps each example isolated, but the duplication can really blow up if we want to convert these examples to p5 or to pure JS (without d3) and need to copy the files again. We might want to think about storing CSV data in a central data folder.

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[joeyklee]

Totally agree that this can start to bloat the project, but as a first step I'm happy/fine to keep our examples working in isolation.

Let's a plan for a follow up where we consider the best place to store our static files and data. It might actually be a good moment to consider where we store also our model files 😬 🙈

Thanks so much!