[Consumption] az consumption budget create: Add command example (#31553)

Author: cxznmhdcxz

src/azure-cli/azure/cli/command_modules/consumption/_help.py

@@ -20,6 +20,9 @@
 helps['consumption budget create'] = """
 type: command
 short-summary: Create a budget for an Azure subscription.
+examples:
+  - name: Create a cost-based monthly budget with a specified amount, start date, and end date.
+    text: az consumption budget create --budget-name "costbudget" --category "cost" --amount 100.0 -s "xxx" -e "xxx" --time-grain "monthly"
 """
 
 helps['consumption budget delete'] = """