Handle agent_boot_time option

Change-Id: Ieaf178979a1e31bd62c922cc2bb1b12147ff2cec
Related-Prod: https://mirantis.jira.com/browse/PROD-24038
diff --git a/README.rst b/README.rst
index f5169b5..ea1e1ec 100644
--- a/README.rst
+++ b/README.rst
@@ -29,6 +29,7 @@
         root_helper_daemon: false
         dhcp_lease_duration: 600
         firewall_driver: iptables_hybrid
+        agent_boot_time: 180
         bind:
           address: 172.20.0.1
           port: 9696