Update stale examples

[jarulsamy]

Hi,

Some of the examples are no longer working. For example, pi-mpich.yaml refers to docker image tags that no longer exist. In addition, it would be really nice if we had some larger examples (similar to the tensorflow ones) that don't need a GPU.

If there are no objections, I am happy to get a PR put together for this myself.

[terrytangyuan]

Feel free to submit PRs!

[tenzen-y]

Regarding pi-mpich.yaml, the image isn't outdated. Although we release the example images every release, the image hasn't yet been released since the MPICH implementation was contributed recently. This means that we don't have any releases for the MPICH implementation.