Add dataset columns to README

README.md

@@ -23,6 +23,12 @@ For the first dataset I will complile only the southern and richer northern stat
 - Punjab
 - West Bengal
 
+## Columns in the dataset
+- state: State codes
+- start_year: Start of the assessment year
+- end_year: End of the assessment year
+- value: Value in INR Lacs - 1 Lac is 100000 INR
+
 ### Sources:
 - 1961 - 1984 : [https://mospi.gov.in/sites/default/files/press_releases_statements/Estimates_of_SDP_1960-61_to_1983-84.pdf](https://mospi.gov.in/sites/default/files/press_releases_statements/Estimates_of_SDP_1960-61_to_1983-84.pdf)
 - 1993-94 to 05-06: [https://mospi.gov.in/publication/state-domestic-product-state-series-1993-94](https://mospi.gov.in/publication/state-domestic-product-state-series-1993-94)