Add entries in changelog

Author: cderv

news/changelog-1.6.md

@@ -14,7 +14,9 @@ All changes included in 1.6:
 
 ## `revealjs` Format
 
-- Update to Reveal JS 5.1.0
+- Update to Reveal JS 5.1.0.
+- Prevent empty SASS built css file to be included in header.
+- Remove wrong `sourceMappingUrl` entry in SASS built css.
 - ([#7715](https://github.com/quarto-dev/quarto-cli/issues/7715)): Revealjs don't support anymore special Pandoc syntax making BulletList in Blockquotes become incremental list. This was confusing and unexpected behavior. Supported syntax for incremental list is documented at <https://quarto.org/docs/presentations/revealjs/#incremental-lists>.
 - ([#9742](https://github.com/quarto-dev/quarto-cli/issues/9742)): Links to cross-referenced images correctly works.