doc PG 17 relnotes: add incremental JSON parser item

Reported-by: Andrew Dunstan

Discussion: https://postgr.es/m/e48dbf1e-62c9-4dbb-8b42-bb9ed898a0ab@dunslane.net

Backpatch-through: master

doc/src/sgml/release-17.sgml

@@ -2451,6 +2451,17 @@ User-defined data type receive functions will no longer receive their data null-
 </para>
 </listitem>
 
+<!--
+Author: Andrew Dunstan <andrew@dunslane.net>
+2024-04-04 [3311ea86e] Introduce a non-recursive JSON parser
+-->
+
+<listitem>
+<para>
+Add incremental JSON parser for use with huge JSON documents (Andrew Dunstan)
+</para>
+</listitem>
+
 <!--
 Author: Nathan Bossart <nathan@postgresql.org>
 2024-02-28 [363eb0599] Convert README to Markdown.