Update tower_host.py (#49186)

<!--- Your description here -->
Current example does not show how to declare variables
+label: docsite_pr

lib/ansible/modules/web_infrastructure/ansible_tower/tower_host.py

@@ -59,6 +59,8 @@ EXAMPLES = '''
     inventory: "Local Inventory"
     state: present
     tower_config_file: "~/tower_cli.cfg"
+    variables:
+      example_var: 123
 '''