Followup updates to Contributing info

[chalin]

This is a tracker issue, following up on:

• Add style guide and basic contribution section #3651

Tasks

• Wrap up Contribution guidelines needs rework or should be dropped #897 by consolidating any remaining content of https://opentelemetry.io/docs/contribution-guidelines/ into the main Contributing page
• Fix aliases to avoid 404s:
  • Add missing alias to acknowledgements.md #3768
  • /docs/contribution-guidelines/ was already defined as an alias is Add style guide and basic contribution section #3651, but the page still exists (and the rewrite isn't specified as an override 301!), so we'll need to wait for the page to be removed.
• Discuss and address, if necessary: https://github.com/open-telemetry/opentelemetry.io/pull/3651/files#r1448798236
• Set appropriate CODEOWNERS for the new folder

/cc @theletterf

[theletterf]

Sounds like the best codeowners for this folder are... us (docs maintainers / approvers)? Unless there's a wider community group for this kind of content.

[chalin]

Right. (I'm unsure why the default rules aren't getting picked up.)

[theletterf]

@chalin #3846 should check all the remaining boxes.

[chalin]

Nice, thanks @theletterf!