docs(grid): biff exporting limitation

Author: Marin Bratanov

controls/grid/functionality/exporting/export-formats/excel-biff-export.md

@@ -175,3 +175,5 @@ newSheet.Cells(1, 1).Value = "NEW CELL"
 * No hierarchy support
 
 * No automatic column/row resizing
+
+* Columns that do not have `HeaderStyle.Width` set do not populate the `Columns` collection of the `Table` in the `ExportInfrastructure`. Read more here: [https://feedback.telerik.com/Project/108/Feedback/Details/226862](https://feedback.telerik.com/Project/108/Feedback/Details/226862). This can cause `e.ExportInfrastructure.Tables[0].Columns.Count` to return `0` or an unexpected number smaller than the number of columns, so that you cannot loop through the columns and apply custom styling to them.