Two missing requirements in Windows. And an UTF-8 code change.

[zhm86]

In Windows, you should add plotly to requirements.txt.
You have to specify altair to version 4 or 4.x.x

Line 88 in build_index.py have to be changed to
with open(f"{OCR_RESULTS_DIR}/{f}", 'r', encoding='utf-8') as fd:
to avoid encoding problem.