On Encouraging Dask users to star the gh repo

@mrocklin issued a [PR](https://github.com/dask/dask.github.io/pull/28) to dask.org that adds a GH star icon.

I think this is a good idea and wanted to raise the issue of encouraging Dask users to star the repo.

I know that GH stars are a bit of a silly metric bu I've also seen people time and time again use it as a proxy for popularity (a recent example is [here](https://towardsdatascience.com/scaling-pandas-comparing-dask-ray-modin-vaex-and-rapids-c74c85a4e59c)).

I'm wondering what else we could do. Any thoughts?

One idea is to include an instruction to star the repo, if you use Dask, in [this tutorial](https://github.com/dask/dask-tutorial), and encourage those who teach Dask at conferences, etc... to mention this.

Another idea is an explicit call to star in the docs.

Another is to tweet it out occasionally.

All these have differing levels of potential obtrusiveness and I want to be sensitive to that also.

Interested in all your thoughts!