DOC add results cache cleanup hint

[romanlutz]

Describe the issue linked to the documentation

We have people running into issues with DuckDB semi-frequently where the solution is essentially to delete the results folder.

We should have small doc page (markdown) that explains what's going on (likely a small change to the DB) and how to fix it (delete results folder). This has to be specific per installation type since the results folder will reside in different places.

cc @donebydan