Specify dependencies

[h-vetinari]

py-rouge depends at least on nltk and - if I understand correctly - also on bsddb3 - these should be specified as dependencies somewhere (e.g. in setup.py or pyproject.toml or requirements.txt, ...).

Sidenote: bsddb3 will not be supported in python >=3.10 anymore, and users should migrate to berkeleydb.

[saprativa]

agreed