add QBO and "raw manifests" guides table

[thesuperzapper]

Based on my comments in #3672 (comment), I think there is a need to distinguish "guides" from distributions.

To help @alexeadem get a presence on the website, I think QBO can be the first such guide.

All other existing distributions have forked the kubeflow/manifests repo, and made at least some platform-specific changes. We can discuss if any of the existing "packaged distributions" should be moved to the "guides for specific platforms" table in future PRs.

Changes

• Adds a "guides for specific platforms" section under "raw kubeflow manifests"
• Adds QBO to the "guides for specific platforms" table
• Moves the "packaged distributions note" to the bottom of the "packaged distributions" section:
  • this is an unrelated change, but I think it makes the page more readable, as it currently interrupts the reader a lot

Screenshot

[google-oss-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: thesuperzapper
Once this PR has been reviewed and has the lgtm label, please assign terrytangyuan for approval. For more information see the Kubernetes Code Review Process.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[thesuperzapper]

@andreyvelich @james-jwu @jbottum based on my comments in #3672 (comment), I think it makes more sense to introduce a "platform-specific guides" section under "raw kubeflow manifests" so we can include things which really aren't "packaged distributions" on the website.

The first one can be the QBO guide.

See the screenshot above.