Cannot run `--help`

I may be missing some steps... I am trying to send a pull request for installation instructions in the README, but I just can't quite get the setup right. Here is what I thought I needed to do to get this setup (and all of these finished successfully):

```
make venv
make install
make setup
```

However, when I try to run the help, I get:

```
➜ make run_help
"havoc_venv"/bin/python havoc/app.py --help
Traceback (most recent call last):
File "havoc/app.py", line 20, in
from havoc.config import Config
ModuleNotFoundError: No module named 'havoc.config'
make: *** [run_help] Error 1
```

I can't find a `havoc/config` dir in the code, though. Maybe I'm doing this wrong, but any help would be appreciated!

Thanks,
Fil

Start with the Makefile targets used by `make venv`, `make install`, `make setup`, and `make run_help`, then inspect `havoc/app.py` and the README installation instructions. Reproduce the setup from a clean environment and determine why `havoc.config` cannot be imported; done means the documented steps allow `make run_help` to complete successfully.

Written by the indexing model from the issue text.