add command example

Author: cxznmhdcxz

src/virtual-wan/azext_vwan/_help.py

@@ -183,6 +183,10 @@
 helps['network vwan create'] = """
     type: command
     short-summary: Create a virtual WAN.
+    examples:
+      - name: Create a virtual WAN.
+        text: |
+            az network vwan create -g MyRG -n MyVwan
 """
 
 helps['network vwan list'] = """