updates with pdf docs

docs/source/products/data/inaf_cpcp_superdarn_datacube.rst

@@ -4,10 +4,12 @@ INAF SuperDARN Cross Polar Cap Potential
 
 .. contents:: The tiny table of contents
 
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
 SuperDARN maximum potential difference measured across the polar caps.
 
+:download:`Further readings (pdf) <../docs/inaf_cpcp_superdarn_datacube-SuperDARN_data_handling.pdf>`.
+
+
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 **Providers**:
 
 - **SupeDARN radars British Antarctic Survey repository** - sources: