Add more details to the security policy

[Wadeck]

The details will be helpful to better guide reporters about what is expected. The separation between docker layer and third party layer was not done in the original version.

Desired reviews from @daniel-beck @dduportal

Testing done

N/A

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• [n/a] Link to relevant issues in GitHub or Jira
• [n/a] Link to relevant pull requests, esp. upstream and downstream changes
• [n/a] Ensure you have provided tests - that demonstrates feature works or fixes the issue

[MarkEWaite]

Looks good to me.

[MarkEWaite]

@dduportal can you review this when you have time? I think it is the right text to include in the documentation.

[dduportal]

That is a legit and clear change to the reporting process and should help a lot! Thanks!