Add availability to ensure nodes moved from enroll to available

Starting from Ironic API microversion 1.11 newly-created nodes
added in enroll state. To move all nodes from enroll state to
available the following pillar might be used:

  ironic:
    client:
      node_state_transition:
        enabled: true
        enroll_to_available:
          provision_state: 'enroll'

Change-Id: If2249ba17eb3c4b89079a78fbd14b129ef80ed01
diff --git a/README.rst b/README.rst
index 44c8b67..6502a63 100644
--- a/README.rst
+++ b/README.rst
@@ -193,3 +193,19 @@
             enabled: true
             strategy: ENCRYPT
             secret_key: secret
+
+Ensure nodes are in target state (available).
+Starting from 1.11 API microversion newly-created node is moved to `enroll`
+state. To move it to available the following client pillar might be used:
+
+.. code-block:: yaml
+
+  ironic:
+    client:
+      node_state_transition:
+        enabled: true
+        enroll_to_available:
+          provision_state: 'enroll'
+          pool_size: 5
+          sleep_time: 10
+          timeout: 15