Document: Documentation for preliminary data structure

[FanWangEcon]

Documentation for core data structure

Document core population files

Document core climate file

Document additional files

• @szkaifeng Describe why clean_data/df_era5_utci_china_1990_hour_decomp2020.csv and clean_data/df_era5_utci_china_2020_hour_decomp1990.csv are needed for running the decomposition file.
• @szkaifeng Why is the clean_data/df_era5_utci_china_2020_hour.csv file almost twice as large as the clean_data/df_era5_utci_china_1990_hour.csv file, does this relate to 2020 having more locations? The time units are the same "number of columns", but 2020 has more rows?