Add ability to ignore deployed machines in wait_for_ready state

Fixes: PROD-33758

Change-Id: I9ada6415ead91fa5e9bc9c0ff7422f61e16ecd03
diff --git a/README.rst b/README.rst
index ffd84f7..a10c96b 100644
--- a/README.rst
+++ b/README.rst
@@ -803,6 +803,21 @@
         - cmd: maas_login_admin
       ...
 
+It is also possible to skip all the machines which are already in
+the "Deployed" state. This is especially useful when you are adding
+new nodes and you don't want to check the already deployed ones.
+This can be enabled by setting in the ``ignore_deployed_machines``
+parameter to ``true`` in reclass.
+
+.. code-block:: bash
+
+    ...
+
+    maas:
+      region:
+        ignore_deployed_machines: true
+      ...
+
 List of available ``req_status`` defined in global variable:
 
 .. code-block:: python