[master] Add missing ChangeLog entry for #1756

ChangeLog

@@ -1,3 +1,10 @@
+577.	[func]		muks
+	Added an SQLite3 index on records(rname, rdtype). This decreases
+	insert performance by ~28% and adds about ~20% to the file size,
+	but increases zone iteration performance. As it introduces a new
+	index, a database upgrade would be required.
+	(Trac #1756, git 9b3c959af13111af1fa248c5010aa33ee7e307ee)
+
 576.	[bug]		tmark, tomek
 	b10-dhcp6: Fixed bug when the server aborts operation when
 	receiving renew and there are no IPv6 subnets configured.