Update README.md

changed warning to be a GitHub alert.

Author: mikala-nsidc

notebooks/ICESat-2_MODIS_Arctic_Sea_Ice/README.md

@@ -1,4 +1,5 @@
-# Warning:  Data access is no longer possible using the method described in this tutorial
+> [!WARNING]  
+> Data access is no longer possible using the method described in this tutorial
 
 This tutorial was developed for a workshop presented at AGU 2019 and represents a snapshot in time.  The data access method described below was developed to access data within NSIDC DAAC’s legacy, on-premises archive.  Data have since migrated to the NASA Earthdata Cloud and are not accessible as described below.  NASA Earthdata Cloud data are freely accessible for download or in-region (AWS us-west-2) access to anyone with an Earthdata Login.  We are developing material to replace the instructions presented here.  In the meantime, we recommend the following tutorials for programmatic data access: