doc(release): aligning version numbering with rest of CN5G

Signed-off-by: Raphael Defosseux <raphael.defosseux@eurecom.fr>

CHANGELOG.md

 # RELEASE NOTES: #
 
-## v1.2.0 -- October 2021 ##
+## v1.2.1 -- October 2021 ##
 
 * Initial Public Release
 * Full support for Ubuntu18 and RHEL7
 * CI Build support
+* Tutorial validated
 
 ## v1.0.0 -- January 2021 ##