DOCSP-13407: [Charts] release notes for 1.20.2 (#438)

Author: steveren

source/release-notes.txt

@@ -10,6 +10,22 @@ MongoDB Charts Cloud Release Notes
    :depth: 1
    :class: twocols
 
+|charts| v1.20.2
+----------------
+
+*Released December 1, 2020*
+
+Bug fixes in this release:
+
+- Fixes an issue where :ref:`donut charts <donut-chart-ref>` constructed
+  from multiple fields failed to render.
+
+- Fixes an issue where :ref:`series <multi-series-charts>` could render in
+  an unpredictable order when using :ref:`string binning <nominal-binning>`.
+
+- Fixes an issue where :ref:`area charts <line-area-chart-ref>` showed
+  overlapping segments when some series had no data for some categories.
+
 |charts| v1.20.1
 ----------------