add cli.md for serialconsole (#8401)

Author: 00Kai0

specification/serialconsole/resource-manager/readme.cli.md

@@ -0,0 +1,15 @@
+## CLI
+
+These settings apply only when `--cli` is specified on the command line.
+
+``` yaml $(cli)
+cli:
+  cli-name: serialconsole
+  package-name: azure-mgmt-serialconsole
+  namespace: azure.mgmt.serialconsole
+  test-scenario:
+    - name: Get the Serial Console disabled status for a subscription
+    - name: List all Serial Console management operations supported by Serial Console RP
+    - name: Disable Serial Console for a subscription
+    - name: Enable Serial Console for a subscription
+```