Regardless of whether it will be used, the config must exist

The order of conditions must check for the existence of the config
file, otherwise new users will not be told what the problem is.
Update Initial Usage to include the `--no-download` flag for conversion

Otherwise the initial conversion will always fail, and eat your zip
file to boot.
Merge pull request #20 from pdf/fix_initial_usage

Fix initial usage (code and docs)