feat(Fluent theme): updateing the change log

Author: MPopov

CHANGELOG.md

@@ -5,6 +5,28 @@ All notable changes for each version of this project will be documented in this
 ## 8.1.0
 
 ### New Features
+
+##### New theme
+Ignite UI for angular now have a new theme that mimics the Microsoft Fluent design as much as possible.  
+In order to use the theme you have to use one of the following mixins:  
+  `igx-fluent-theme` and `igx-fluent-dark-theme`  
+  
+We also added two new pallets that go with the new theme, `$fluent-word-palette` and `$fluent-excel-palette`.  
+  
+This is an example of how you can use the new theme.
+
+```scss
+// Light version
+.fluent-word-theme {
+    @include igx-fluent-theme($fluent-word-palette);
+}
+
+// Dark version
+.fluent-excel-dark-theme {
+    @include igx-fluent-dark-theme($fluent-excel-palette);
+}
+```
+
 - `IgxBottomNav` now supports an `igx-tab` declaration mode. When in this mode, panels declarations are not accepted and tab items' content is not rendered.
     - You can use this mode to apply directives on the tab items - for example to achieve routing navigation.
     - You are allowed to customize tab items with labels, icons and even templates.