docs(common): add info for changes that was missed initially

Author: marin-bratanov

upgrade/breaking-changes/2-0-0.md

@@ -60,6 +60,10 @@ Telerik.Blazor.Size -> Telerik.Blazor.WindowSize
 
 This is a list of the components that had methods removed and the new approach of doing things.
 
+### Button
+
+* The `IsIconButton` property is removed. It was never supposed to be public and is set internaly by the component when it has no text.
+
 ### Calendar
 
 * The `Navigate()` method is no longer available in favor of two-way binding for the `View` and `Date` parameters. An example is avalable in the [Navigate]({%slug components/calendar/navigation%}#programmatic-navigation) article.
@@ -74,6 +78,7 @@ This is a list of the components that had methods removed and the new approach o
 * The standalone icon component is now in the `Telerik.Blazor.Components.Common.Icon` namespace.
 * The `IconName` property is now `Icon`.
 * The `Class` property is now `IconClass`.
+* If you want to use the Telerik icons together with custom classes, you must ammend those classes instead of using the `Icon` property. For example, `<TelerikIcon IconClass="@("my-class k-icon k-i-" + IconName.File )" />`.
 
 ### Grid