doc: PG 14 relnotes, mention CONCURRENTLY improvements

Add items for vacuum not having to wait for CONCURRENTLY, and
CONCURRENTLY not having to wait for other CONCURRENTLY operations.

Reported-by: Simon Riggs

Discussion: https://postgr.es/m/CANbhV-EMM4nf7Ys-Yae_kY25dXT_3eiOXke2+yw44jgy+4jNsA@mail.gmail.com

Backpatch-through: 14 only

doc/src/sgml/release-14.sgml

@@ -744,6 +744,28 @@ Author: Peter Geoghegan <pg@bowt.ie>
 
       <listitem>
 <!--
+Author: Alvaro Herrera <alvherre@alvh.no-ip.org>
+2020-11-25 [c98763bf5] Avoid spurious waits in concurrent indexing
+Author: Alvaro Herrera <alvherre@alvh.no-ip.org>
+2021-01-15 [f9900df5f] Avoid spurious wait in concurrent reindex
+Author: Alvaro Herrera <alvherre@alvh.no-ip.org>
+2021-02-23 [d9d076222] VACUUM: ignore indexing operations with CONCURRENTLY
+-->
+
+       <para>
+        Allow vacuum to be more aggressive in removing dead rows during
+        minimal-locking index operations (Álvaro Herrera)
+       </para>
+
+       <para>
+        Specifically, <command>CREATE INDEX CONCURRENTLY</command> and
+        <command>REINDEX CONCURRENTLY</command> no longer limit the dead
+        row removal of other relations.
+       </para>
+      </listitem>
+
+      <listitem>
+<!--
 Author: Fujii Masao <fujii@postgresql.org>
 2020-12-08 [e2ac3fed3] Speed up rechecking if relation needs to be vacuumed or 
 -->
@@ -2283,6 +2305,23 @@ Author: Michael Paquier <michael@paquier.xyz>
       </para>
      </listitem>
 
+      <listitem>
+<!--
+Author: Alvaro Herrera <alvherre@alvh.no-ip.org>
+2020-11-25 [c98763bf5] Avoid spurious waits in concurrent indexing
+Author: Alvaro Herrera <alvherre@alvh.no-ip.org>
+2021-01-15 [f9900df5f] Avoid spurious wait in concurrent reindex
+Author: Alvaro Herrera <alvherre@alvh.no-ip.org>
+2021-02-23 [d9d076222] VACUUM: ignore indexing operations with CONCURRENTLY
+-->
+
+       <para>
+        Allow index commands using <command>CONCURRENTLY</command> to
+        avoid waiting for the completion of other operations using
+        <command>CONCURRENTLY</command> (Álvaro Herrera)
+       </para>
+      </listitem>
+
      <listitem>
 <!--
 Author: Tom Lane <tgl@sss.pgh.pa.us>