add doc for retry

docs/run_test/runbook.rst

@@ -66,6 +66,8 @@ Runbook Reference
 
    -  `environment <#environment>`__
 
+      -  `retry <#retry>`__
+
       -  `environments <#environments>`__
 
          -  `name <#name-4>`__
@@ -670,6 +672,11 @@ environment
 List of environments. For more information, refer to
 :ref:`write_test/concepts:node and environment`.
 
+retry
+^^^^^^^^^^^^
+
+Number of retry attempts for failed deployments, default value is 0.
+
 environments
 ^^^^^^^^^^^^