add changelog entry for richtext change

CHANGELOG.txt

@@ -16,6 +16,7 @@ Changelog
  * Added document_served signal which gets fired when a document is downloaded
  * Added translation for Portuguese Brazil
  * Made compatible with Python 2.6
+ * 'richtext' template filter now wraps output in <div class="rich-text"></div>, to assist in styling
  * Fix: non-ASCII characters in image filenames are now converted into ASCII equivalents rather than becoming all underscores
  * Fix: paths to fonts and images within CSS are no longer hard-coded to /static/
  * Fix: Localization files for the JQuery UI datepicker are stored locally and only imported when a localization is known to be available