Add gh-pages Readme

[scottrigby]

What this PR does / why we need it:

Friendly landing page for end users who may browse to https://kubernetes.github.io/kube-state-metrics.

Once merged, it would look similar to https://prometheus-community.github.io/helm-charts/

[scottrigby]

Depends on kubernetes/test-infra#20291

[cpanato]

/lgtm

[scottrigby]

/restest

[scottrigby]

force pushing to trigger re-checking if the configs from kubernetes/test-infra#20291 have propagated

[cpanato]

tests will run only for master and release branches
https://github.com/kubernetes/kube-state-metrics/blob/master/.github/workflows/ci.yml#L13

[scottrigby]

👍 we don't want actions to run on the gh-pages branch. For future ref, what I was testing by re-pushing is whether those checks were still configured as Required. They appear to be (screenshot below). Opened a follow-up PR in test-infra to remove them: kubernetes/test-infra#20322

[tariq1890]

/approve

[scottrigby]

kubernetes/test-infra#20426 appears to have worked 👍

tide just needs approved, lgtm labels again, then we should be good to go.

[scottrigby]

/assign @tariq1890

[cpanato]

/lgtm

[mrueg]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: cpanato, mrueg, scottrigby, tariq1890
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[mrueg]

@cpanato @scottrigby do we need to add an OWNERS file on the gh-pages branch or is that something that needs to be fixed on test-infra side?

[scottrigby]

@mrueg That's a good question. I think that depends on how we want to handle this. A repo admin should now be able to merge this PR to the gh-pages branch directly, without prow. If we want to use prow for direct merges to gh-pages (for PRs like this, which aren't automated from PRs to master), I think you may be right about an OWNERS file. Let's try to get this right. I'll open a question in k8s slack #github-management now.

[scottrigby]

Slack convo started: https://kubernetes.slack.com/archives/C01672LSZL0/p1610380054131300 I'm giving a talk today, so I may have to circle back to this later in the day.

[tariq1890]

@scottrigby Thanks for this PR.

I am okay with manually merging this as a one-off right now, but I think it's better to incorporate as much automation as we can to this branch as well.

[scottrigby]

@tariq1890 re automation I had set up README sync github action here https://github.com/prometheus-community/helm-charts/blob/main/.github/workflows/sync-readme.yaml and here helm/charts#23921, both of which have worked well. I didn't do that for this repo but could do in a follow-up PR.