overview.md: Fixed three broken links in the overview.md file.

[joecus1]

Pull Request

Issue Number: Closes #512

Summary

Fixes three broken links within overview.md file.

Changes

• Link for getting started changed to quickstart.md file so that overview.md file does not link to itself
• Links for adopters.md and contributing.md fixed (relative path was incorrect for these)

Checklist

• [x ] Local Tests Passing?
• [x ] CICD and Pipeline Tests Passing?
• [x ] Added any new Tests?
• [x ] Documentation Updates Made?
• [x ] Are there any API Changes? If yes, please describe below.
• [x ] This is not a breaking change. If it is, please describe it below.

Are there API Changes?

No

Is this a breaking change?

No

Anything else?

This is only a change to documentation.

Other comments, collaborators, etc.

[danuw]

@joecus1 hi, we need DCO to pass. Would you be able to look at the details of the issue in the workflows and apply the requested changes please?

This might be the link but otherwise take it from "Details" link in as shown in the attached screenshot https://github.com/Green-Software-Foundation/carbon-aware-sdk/pull/513/checks?check_run_id=24658759137

[joecus1]

Going to resubmit this so that DCO passes