doc:  PG 12 relnotes - add item about amcheck index root check
Reported-by: Peter Geoghegan
Discussion:
Backpatch-through: 12
@@ -3228,6 +3228,18 @@ Author: Tom Lane <tgl@sss.pgh.pa.us>
<listitem>
<!--
+Author: Peter Geoghegan <pg@bowt.ie>
+2019-03-20 [c1afd175b] Allow amcheck to re-find tuples using new search.
+-->
+
+ <para>
+ Add a parameter to a <xref linkend="amcheck"/> function to check
+ each index tuple from the root of the tree.
+ </para>
+ </listitem>
+
+ <listitem>
+<!--
Author: Michael Paquier <michael@paquier.xyz>
2018-08-28 [1aaf532de] Rework option set of oid2name
Author: Michael Paquier <michael@paquier.xyz>
