Error if -r used without target directory

[jayvdb]

$ pip2pi -r /path/to/requirements.txt
ERROR: Invalid requirement: '/path/to/requirements.txt'
It looks like a path. It does exist. The argument you provided (/path/to/requirements.txt) appears to be a requirements file. If that is the case, use the '-r' flag to install the packages specified within it.
Traceback (most recent call last):
  File "/usr/bin/pip2pi", line 11, in <module>
    load_entry_point('pip2pi==0.8.0', 'console_scripts', 'pip2pi')()
  File "/usr/lib/python3.7/site-packages/libpip2pi/commands.py", line 558, in pip2pi
    res = pip2tgz(subcmd_argv)
  File "/usr/lib/python3.7/site-packages/libpip2pi/commands.py", line 94, in maintain_cwd_helper
    return f(*args, **kwargs)
  File "/usr/lib/python3.7/site-packages/libpip2pi/commands.py", line 443, in pip2tgz
    pip_run_command(pip_download_command.split() + [outdir] + argv[2:])
  File "/usr/lib/python3.7/site-packages/libpip2pi/commands.py", line 191, in pip_run_command
    %(res, pip_args))
libpip2pi.commands.PipError: pip failed with status 1 while running: ['download', '--dest', '/path/to/cwd/-r', '/path/to/requirements.txt']