update changelog for release

Author: isaisabel

CHANGELOG.md

@@ -1,5 +1,6 @@
-# Changes staged on develop
+# v1.6 - 5 October 2020
 ## Improvements
+- Added [layer to SVG](https://github.com/mitre-attack/attack-scripts/tree/master/layers#to_svgpy) converter. See issue [#1](https://github.com/mitre-attack/attack-scripts/issues/1).
 - Added option to filter mappings by tactic in [technique_mappings_to_csv](technique_mappings_to_csv.py). See pull request [#46](https://github.com/mitre-attack/attack-scripts/pull/46).
 
 # v1.5.2 - 2 September 2020