docs: Clarify pg_ctl initdb option text to match options proto.

The options string appeared in PG 10.

Reported-by: pgsql-kr@postgresql.kr

Discussion: https://postgr.es/m/153500377658.1378.6587007319641704057@wrigleys.postgresql.org

Backpatch-through: 10

doc/src/sgml/ref/pg_ctl-ref.sgml

@@ -334,7 +334,7 @@ PostgreSQL documentation
         options being passed through.
        </para>
        <para>
-        The <replaceable>options</replaceable> should usually be surrounded by single or
+        The <replaceable>initdb-options</replaceable> should usually be surrounded by single or
         double quotes to ensure that they are passed through as a group.
        </para>
       </listitem>