Improve error message when we can't find hass config dir

[balloob]

In db_from_hass_config, when config.find_hass_config() raises a ValueError, we should print instructions on how a user should manually create a db instance from their DB url.

https://github.com/robmarkcole/HASS-data-detective/blob/a2f09225a577fc6152c5c7d47b439833f578fba2/detective/core.py#L17