Added convert-to-cabal and stern docs to /docs.

[elland]

I keep getting lost trying to find specific docs because… they're not under docs/. I didn't want to do an exhaustive check before making sure we want this, or what we have planned for docs, considering all the legacy stuff.

Checklist

• The PR Title explains the impact of the change.
• The PR description provides context as to why the change should occur and what the code contributes to that effect. This could also be a link to a JIRA ticket or a Github issue, if there is one.