Add to the changelog from jupyter-widgets#1279.

Author: jasongrout

docs/source/changelog.md

@@ -27,6 +27,11 @@ Major user-visible changes in ipywidgets 7.0 include:
 - A new Password widget, which behaves exactly like the Text widget, but hides the typed text: `Password()`. ([#1310](https://github.com/jupyter-widgets/ipywidgets/pull/1310))
 - A new SelectionRangeSlider widget for selecting ranges from ordered lists of objects. For example, this enables having a slider to select a date range. ([#1356](https://github.com/jupyter-widgets/ipywidgets/pull/1356))
 - The documentation theme is changed to the new standard Jupyter theme. ([#1363](https://github.com/jupyter-widgets/ipywidgets/pull/1363))
+- The description width is now configurable with the `.style.description_width` attribute ([#1376](https://github.com/jupyter-widgets/ipywidgets/pull/1376))
+- Selection containers (tabs, accordions) now have the convention that a `.selected_index` of `None` means no container is selected ([#1495](https://github.com/jupyter-widgets/ipywidgets/pull/1495))
+- ToggleButtons have a new `.style.button_width` attribute to set the CSS width of the buttons. Set this to `'initial'` to have buttons that individually size to the content width. ([#1257](https://github.com/jupyter-widgets/ipywidgets/pull/1257))
+
+
 
 Major changes developers should be aware of include:
 
@@ -39,6 +44,7 @@ Major changes developers should be aware of include:
 - A custom serializer is given the widget instance as its second argument, and a custom deserializer is given the widget manager as its second argument.
 - The widget manager `clear_state` method no longer has a `commlessOnly` argument. All models in the widget manager will be closed and cleared when `clear_state` is called. ([#1354](https://github.com/jupyter-widgets/ipywidgets/pull/1354))
 - The python `ipywidget.domwidget.LabeledWidget` is now `ipywidget.widget_description.DescriptionWidget`, and there is a new `ipywidget.widget_description.DescriptionStyle` that lets the user set the CSS width of the description.
+- The model `.id` attribute has been renamed to `.model_id` to avoid conflicting with the Backbone `.id` attribute. ([#1410](https://github.com/jupyter-widgets/ipywidgets/pull/1410))
 
 6.0
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