Adding #191 to changelog

Author: IanDavila

CHANGELOG.md

@@ -34,6 +34,7 @@
 ## ATT&CK Website version 2.1.1
 ### Improvements
 - Improved matrix page header layout with versioning feature. See issue [#190](https://github.com/mitre-attack/attack-website/issues/190).
+- Added versioning feature to tour. See issue [#191](https://github.com/mitre-attack/attack-website/issues/191).
 
 # Sub-techniques Beta
 ## ATT&CK Website version 2.1