Add requirements.txt

[cr-xu]

Hi,
I noticed that there is no requirements file in the repo.
Several packages are needed to run the sample. It would be nice if one can just install all of them via
pip install -r requirements.txt

E.g. a simple pip freeze gives the following:

cycler==0.10.0
joblib==0.17.0
kiwisolver==1.2.0
matplotlib==3.3.2
numpy==1.19.2
pandas==1.1.3
Pillow==7.2.0
pyparsing==2.4.7
PyQt5==5.15.1
PyQt5-sip==12.8.1
pyqtgraph==0.11.0
python-dateutil==2.8.1
pytz==2020.1
scikit-learn==0.23.2
scipy==1.5.2
six==1.15.0
sklearn==0.0
threadpoolctl==2.1.0