fix: build wheel by requirements.txt not pack

[ValMystletainn]

Thanks for the convenient and amazing collection for all the grad-cam based method.
You just published the 1.4.7 version in June, 15, 2023. As for the changing in setuptool, people cannot install the from pip install grad-cam right now.

It will come into a build failure in wheel like this

1. on macos

2. on linux

the setup.py need requirement.txt as usual, but the setuptools changing in recent half years make it not pack requirement.txt anymore.
This PR is a fast and minial fixing, just adding a config file reading by wheel builder to include requirements.txt mannully
If you need I can make a PR to turn the whole package into a modern pakcage tool like poetry with full tests.

Reference:

1. include-requirements-txt-file-in-python-wheel: https://stackoverflow.com/questions/38533669/include-requirements-txt-file-in-python-wheel
2. setuptools not support the MANIFEST.in setting yet: [FR] Support specifying MANIFEST.in config via pyproject.toml pypa/setuptools#3341
3. poetry setting: https://python-poetry.org/docs/pyproject/#include-and-exclude