wrap <xxx> in backticks for better documentation (Azure#2016)

src/spring-cloud/azext_spring_cloud/_help.py

@@ -235,7 +235,7 @@
 
 helps['spring-cloud app deployment create'] = """
     type: command
-    short-summary: Create a staging deployment for the app. To deploy code or update setting to an existing deployment, use az spring-cloud app deploy/update --deployment <staging deployment>.
+    short-summary: Create a staging deployment for the app. To deploy code or update setting to an existing deployment, use `az spring-cloud app deploy/update --deployment <staging deployment>`.
     examples:
     - name: Deploy source code to a new deployment of an app. This will pack current directory, build binary with Pivotal Build Service and then deploy.
       text: az spring-cloud app deployment create -n green-deployment --app MyApp -s MyCluster -g MyResourceGroup