Adding new documentation(help/contributor/new-docs/_index.md)

[ellenevans]

Expected Behavior

Actual Behavior

Broken link
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The link currently points to a .md file, not the served html.

Steps to Reproduce the Problem

Additional Info

Additional context
Add any other context about the problem here.

Install information:

• Platform (GKE, IKS, AKS, etc.):
• Knative Version:

[RichieEscarez]

This needs to go in knative/website#288