Dependencies for pydensecrf

[Tianzhe Chu]

Stuck in installing pydensecrf just now and finally solved~ This issue is just for the convenience of followers~

cython 3.0.0 currently doesn't support the compilation of pydensecrf and directly runing the following command
pip install git+https://github.com/lucasb-eyer/pydensecrf.git will fail.

Use the following instead:
pip3 install --force-reinstall cython==0.29.36
pip3 install --no-build-isolation git+https://github.com/lucasb-eyer/pydensecrf.git

Reference:
lucasb-eyer/pydensecrf#123 (comment)