[Doc] add link to Frama-C blog post about C-Reduce

doc/userman/user-analysis-scripts.tex

@@ -333,7 +333,10 @@ different. It is available at\\
   C programs causing crashes in \FramaC; useful e.g. when submitting a bug
   report to \FramaC, without needing to submit potentially confidential data.
   The script contains extensive comments about its usage. It is also
-  described in a post from the \FramaC blog.
+  described in a post\footnote{%
+    {\em Debugging Frama-C analyses: better privacy with C-Reduce},
+    at \url{https://pub.frama-c.com/scripts/usability/2020/04/02/creduce.html}.}
+  from the \FramaC blog.
 \end{description}
 
 To use the \texttt{creduce.sh} script, you need to have the C-Reduce tool