Add details of data source for recipe 20

Author: sadielbartholomew

docs/source/recipes/plot_20_recipe.py

@@ -13,7 +13,12 @@
 import cf
 
 # %%
-# 2. Read the fields in:
+# 2. Read the fields in. This dataset consists of depth-averaged eastward and
+# northward current components plus the sea surface height above sea level and
+# is a gridded dataset, with grid resolution of 1.85 km, covering the entire
+# Irish Sea area. It was found via the CEDA Archive at the location of:
+# https://catalogue.ceda.ac.uk/uuid/1b89e025eedd49e8976ee0721ec6e9b5, with
+# DOI of https://dx.doi.org/10.5285/031e7ca1-9710-280d-e063-6c86abc014a0:
 f = cf.read(
     "~/summerstudents/final-recipes/new-required-datasets/POLCOMS_WAM_ZUV_01_16012006.nc")