[Documentation] Add CHANGELOG entries for version 3.6.1.

Signed-off-by: Giacomo Marciani <[email protected]>

Author: gmarciani

CHANGELOG.md

@@ -3,6 +3,13 @@ aws-parallelcluster-cookbook CHANGELOG
 
 This file is used to list changes made in each version of the AWS ParallelCluster cookbook.
 
+3.6.1
+------
+
+**CHANGES**
+- Remove security updates step executed on cluster nodes bootstrap in US isolated regions
+  in order to reduce bootstrap time and avoid a potential point of failure.
+
 3.6.0
 ------