For those encountering installation issues when running pip3 install -r ./requirements.txt, there is a missing line that you need to install first before running the command (or add it to the requirements.txt file):
pip install pypandoc==1.4 (or add pypandoc==1.4 to the requirements file before the pyspark entry)
There is also an issue with the requirement for scipy==1.3.1 when using versions of python higher than 3.6. Need to install scipy 1.4.1 instead.