Improve the Katib (hyperparameter tuning) docs

[sarahmaddox]

The Katib docs on the Kubeflow website don't do justice to the capabilities and UX provided by Katib:
https://www.kubeflow.org/docs/components/hyperparameter-tuning/hyperparameter/

The docs should be more visual, at least providing screenshots to get users oriented. Here's the current Katib starter page:

There are some docs on GitHub which we should merge into the website docs:
https://github.com/kubeflow/katib/

There was also some good content at the Kubeflow contributor summit in October 2019. I can't find any slides/recordings, but we should get hold of them and use them as input.

The Kubeflow v0.7 blog post also has useful info:

The Katib v1alpha3 API includes a new Suggestion CR which tracks the suggestions generated for each trial of an experiment by the corresponding algorithm service. The system architecture has been redesigned to make it more Kubernetes-native with better support for events. The v1alpha3 API also comes with a new metric collector implementation. Users can specify the metric collector type in the experiment config. Currently supported types are StdOutCollector(default), FileCollector and TFEventCollector. The internal database implementation is also refactored to support multiple database backends. This release also supports Prometheus metrics that includes controller runtime metrics and creation/deletion/success/failure counters for experiments and trials.

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[sarahmaddox]

/assign

Starting work on this now.