doc PG 17 relnotes: add item about libpq large data transfers

Reported-by: Jelte Fennema-Nio

Discussion: https://postgr.es/m/CAGECzQTz5aUqLEL6daLd2Hu2FXS_LOSh4keDndJ1fwThsb_b5w@mail.gmail.com

Reviewed-by: Joe Conway

Backpatch-through: master

doc/src/sgml/release-17.sgml

@@ -1901,6 +1901,17 @@ Add libpq function PQsetChunkedRowsMode to allow retrieval of results in chunks
 </para>
 </listitem>
 
+<!--
+Author: David Rowley <drowley@postgresql.org>
+2024-04-07 [c4ab7da60] Avoid needless large memcpys in libpq socket writing
+-->
+
+<listitem>
+<para>
+Allow libpq to more efficiently transfer large blocks of data (Melih Mutlu)
+</para>
+</listitem>
+
 <!--
 Author: Heikki Linnakangas <heikki.linnakangas@iki.fi>
 2024-04-08 [d39a49c1e] Support TLS handshake directly without SSLRequest negoti