Update docstring

inputs/distributions.py

@@ -3,7 +3,11 @@
 This will calculate the values required to generate triangular distributions,
 i.e. 'min', 'mode', and 'max' in the `numpy.random.triang()` function.
 
-The values are written to 'triang-values.csv'
+Reads:
+    'IPCC AR6.xlsx'
+
+Writes:
+    'triang-values.csv'
 
 D. Howe
 d.howe@wrl.unsw.edu.au