Clarifying `B_dict` format and mapping with `Bs`

[leetaiying]

Hi Omar, I hope you're well. I noticed a potential confusion regarding the description of B_dict and its mapping with the rows of Bs in policy_priority_inference.py. Here are the details:

• In the function run_ppi(), the description of B_dict indicates that the values of this dictionary are lists of indices of the expenditure programs, corresponding to the rows of Bs in its matrix form.
• However, from tutorials/01c - data preparation (expenditure).ipynb and tutorials/02 - model calibration.ipynb it appears that the values in B_dict are the expenditure program numbers and not the indices. From source_code/policy_priority_inference.py lines 281 to 318 it looks like as long as the expenditure program numbers and the Bs are sorted the same way, it works correctly.

Could you confirm if this understanding is correct please? Thank you!