Minor cleanup on contributing guide

[anishasthana]

Opening a WIP PR to provide a forum for us to discuss the for community membership guidelines topic.

This set of guidelines is heavily inspired by the Kubernetes guidelines at https://github.com/kubernetes/community/blob/master/community-membership.md?plain=1#community-membership

Closes #736

cc @kubeflow/kubeflow-steering-committee. I'll defer to your expertise/recommendations here!

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[andreyvelich]

This is great @ananth102, thank you for driving this!
I will cc WG leads to review this, and we should follow this guidelines across all Kubeflow projects once we finalize it.

/assign @kubeflow/kubeflow-steering-committee @kubeflow/wg-data-leads @kubeflow/wg-notebooks-leads @kubeflow/wg-training-leads @kubeflow/wg-automl-leads @kubeflow/wg-pipeline-leads @kubeflow/wg-manifests-leads

[andreyvelich]

I think, as part of this initiative, we say that all Kubeflow WGs should follow this process for contributors promotion.
Also, we might want to remove promotion requirements from the WGs charters. For example:

• WG Manifests: https://github.com/kubeflow/community/blob/master/wg-manifests/charter.md#manifests-wg-lead-requirements

[anishasthana]

I've moved all the membership related changes over to kubeflow/website#3827.
@andreyvelich @tarilabs @StefanoFioravanzo @juliusvonkohout @james-jwu fyi!