Improve documentation generation process

[zackbrown]

Related to: https://github.com/helm/helm-www#updating-the-helm-cli-reference-docs , the primary pain points are:

• The manual .md-file-copying process is prone to missing deletions, leading to stale docs (for example: https://github.com/helm/helm/issues/6996#issuecomment-582065733 )
• The manual .md-file-copying process would benefit from scripting

I took a pass at addressing these in this closed PR https://github.com/helm/helm-www/pull/486, but discovered that there was more to the docs-updating process, and that it would likely be better handled by someone who's more plugged into the domain.

Filing here for tracking per conversation with @bacongobbler : https://github.com/helm/helm-www/pull/486#issuecomment-582137998

[mattfarina]

This would be great to have better automation around this.

[bridgetkromhout]

Possibly related: how do we handle translations of the auto-generated docs? See https://github.com/helm/helm-www/pull/802 and https://github.com/helm/helm-www/pull/807.

[bridgetkromhout]

Related to https://github.com/helm/helm/issues/6592.