Update event-hubs-faq.yml

Added another question that has come up in DLs and with customer I'm working with. Seems it's not possible to change a deployed resource from Standard tier to Premium tier (or Premium to Standard).

Author: OrrinEdenfield

articles/event-hubs/event-hubs-faq.yml

@@ -16,6 +16,11 @@ sections:
         answer: |
           A namespace is a scoping container for Event Hub/Kafka Topics. It gives you a unique [FQDN](https://en.wikipedia.org/wiki/Fully_qualified_domain_name). A namespace serves as an application container that can house multiple Event Hub/Kafka Topics. 
           
+      - question: |
+          Is it possible to change pricing tier after deployment?
+        answer: |
+          No. Once deployed, it is not possible to change (for example) from Standard Tier to Premium Tier without deploying a new resource.
+          
       - question: |
           When do I create a new namespace vs. use an existing namespace?
         answer: |