Added more information around backup storage class

Add links and information around RWX storage class

Author: EricBuMSFT

articles/azure-arc/data/release-notes.md

@@ -157,7 +157,7 @@ For complete release version information, see [Version log](version-log.md).
     - Set `--readable-secondaries` to any value between 0 and the number of replicas minus 1.
     - `--readable-secondaries` only applies to Business Critical tier. 
 - Automatic backups are taken on the primary instance in a Business Critical service tier when there are multiple replicas. When a failover happens, backups move to the new primary. 
-- RWX capable storage class is required for backups, for both General Purpose and Business Critical service tiers.
+- [ReadWriteMany (RWX) capable storage class](https://docs.microsoft.com/en-us/azure/aks/concepts-storage#azure-disks) is required for backups, for both General Purpose and Business Critical service tiers. Specifying a non-ReadWriteMany storage class will cause the SQL Managed Instance to be stuck in "Pending" status during deployment.
 - Billing support when using multiple read replicas.
 
 For additional information about service tiers, see [High Availability with Azure Arc-enabled SQL Managed Instance (preview)](managed-instance-high-availability.md).