doc PG 18 relnotes: split apart log_connections item

Also add details to asynchronous I/O item.

Reported-by: Melanie Plageman

Discussion: https://postgr.es/m/CAAKRu_YsVvyantS0X0Y_-vp_97=yGaoYJMXXyCEkR7pumAH3Jg@mail.gmail.com

doc/src/sgml/release-18.sgml

@@ -569,6 +569,7 @@ Add an asynchronous I/O subsystem (Andres Freund, Thomas Munro, Nazir Bilal Yavu
 </para>
 
 <para>
+This feature allows backends to queue multiple read requests, which allows for more efficient sequential scans, bitmap heap scans, and vacuums.
 This is enabled by server variable io_method, with server variables io_combine_limit and io_max_combine_limit added to control it.  This also enables
 effective_io_concurrency and maintenance_io_concurrency values greater than zero for systems without fadvise() support.  The new system view pg_aios shows the file handles being used
 for asynchronous I/O.
@@ -682,15 +683,12 @@ This more accurately reflects modern hardware.
 <!--
 Author: Melanie Plageman <melanieplageman@gmail.com>
 2025-03-12 [9219093ca] Modularize log_connections output
-Author: Melanie Plageman <melanieplageman@gmail.com>
-2025-03-12 [18cd15e70] Add connection establishment duration logging
 -->
 
 <listitem>
 <para>
 Increase the logging granularity of server variable log_connections (Melanie Plageman)
 <ulink url="&commit_baseurl;9219093ca">&sect;</ulink>
-<ulink url="&commit_baseurl;18cd15e70">&sect;</ulink>
 </para>
 
 <para>
@@ -698,6 +696,18 @@ This server variable was previously only boolean;  these options are still suppo
 </para>
 </listitem>
 
+<!--
+Author: Melanie Plageman <melanieplageman@gmail.com>
+2025-03-12 [18cd15e70] Add connection establishment duration logging
+-->
+
+<listitem>
+<para>
+Add log_connections option to report the duration of connection stages (Melanie Plageman)
+<ulink url="&commit_baseurl;18cd15e70">&sect;</ulink>
+</para>
+</listitem>
+
 <!--
 Author: Tom Lane <tgl@sss.pgh.pa.us>
 2025-04-07 [3516ea768] Add local-address escape "%L" to log_line_prefix.