doc: add TrustZone support in the list of key features

This commit includes the basic support for ARM TrustZone-M
in the list of key features for 1.13 release.

Signed-off-by: Ioannis Glaropoulos <[email protected]>

Author: ioannisg

doc/release-notes-1.13.rst

@@ -20,7 +20,7 @@ Major enhancements with this release include:
 * Introduced reworked ADC API and updated Nordic, NXP, Atmel, and Designware
   drivers
 * Support OS driven Power Management framework
-
+* Basic support for Arm TrustZone in Armv8-M
 
 The following sections provide detailed lists of changes by component.