doc: PG 16 relnotes, add psql \df+ source code change

Reported-by: bzm@2bz.de

Discussion: https://postgr.es/m/17957-e1db8b1c15af444a@postgresql.org

doc/src/sgml/release-16.sgml

@@ -2163,6 +2163,21 @@ Add "FOREIGN" designation to psql \d+ for foreign table children and partitions
 </para>
 </listitem>
 
+<!--
+Author: Tom Lane <tgl@sss.pgh.pa.us>
+2023-03-02 [3dfae91f7] Show "internal name" not "source code" in psql's \df+ co
+-->
+
+<listitem>
+<para>
+Prevent \df+ from showing function source code (Isaac Morland)
+</para>
+
+<para>
+Function bodies are more easily viewed with \ev and \ef.
+</para>
+</listitem>
+
 <!--
 Author: Peter Eisentraut <peter@eisentraut.org>
 2022-11-15 [5b66de343] psql: Add command to use extended query protocol