azureblob: add examples for access tier

Azure Blob access tier values are case-sensitive, though this is
not indicated anywhere in the documentation. Adding examples
with proper casing.

docs/content/azureblob.md

@@ -250,6 +250,10 @@ tiering blob to "Hot" or "Cool".
 - Env Var:     RCLONE_AZUREBLOB_ACCESS_TIER
 - Type:        string
 - Default:     ""
+- Examples:
+     - "Hot"
+     - "Cool"
+     - "Archive"
 
 #### --azureblob-disable-checksum