highlight prerequisite step needed for formatting

Without adding columns into view, the formatters won't work properly and have been causing customer ICMs. highlighting some key steps in documentation to avoid confusion.

Author: pKalaga

docs/declarative-customization/view-calendar-formatting.md

@@ -15,13 +15,12 @@ Groups the command bar customization options. For details on `commandBarProps`,
 
 ## See also
 - [Command bar customization syntax reference](./view-commandbar-formatting.md)
+---
+### Pre-requisite : List setup before creating a calendar view and applying a JSON formatting
 
-### List setup before creating a calendar view and applying a JSON formatting
-
-Before creating a new calendar view, a list should include all the required columns to be used in any JSON formatting.
-
-After creating a calendar view, if more columns are required, go to the [List Settings page](https://support.microsoft.com/office/edit-list-settings-4d35793b-246e-42a3-990c-563a83795b7f) to create and add them to a calendar view.
-
+- Before creating a new calendar view, a list should include all the required columns to be used in any JSON formatting.
+- After creating a calendar view, if more columns are required, go to the [List Settings page](https://support.microsoft.com/office/edit-list-settings-4d35793b-246e-42a3-990c-563a83795b7f) to create and add them to a calendar view.
+---
 ### Conditional view formatting based on a specific column
 
 The following image shows an example of conditional formatting applied to a calendar view, based on a single choice column named **PROJECT**: