Write a Explanation Document for a Python Code

I am looking for a freelancer to help me write an explanation document for a Python code. The python code runs time series based analysis. Need basics mathematics knowledge to understand the code. Explain the code part by part in simple english with example calculation. This is the url which has the code https://www.pythonforfinance.net/2018/07/04/mean-reversion-pairs-trading-with-inclusion-of-a-kalman-filter/