Clarification of documentation

[Claire Michailovsky]

In documentation, add a column to the data table to match the variables with the way they are set in the configuration. For example, after VIIRS bt product, the column would contain ‘thermal’.

[bert.coerver]

https://bitbucket.org/cioapps/pywapor/commits/f5538618c479b801071c7bd59f99fc9947fdbca8

https://www.fao.org/aquastat/py-wapor/data_sources.html