Glance cache pruner/cleaner operations via salt

Added:

 - Adding by default cron-job that prunes cache daily if it`s size
more than value set in the `image_cache_max_size` configuration option.
 - Adding by default cron-job that cleans cache that is older than
value in the `image_cache_stall_time period` configuration option.

Change-Id: Ic62a95b66776844faa78d72c2c6b72c5da2d628d
Related-Prod: PROD-21505 (PROD:21505)
diff --git a/README.rst b/README.rst
index 0d49ea7..e9c2d30 100644
--- a/README.rst
+++ b/README.rst
@@ -341,6 +341,34 @@
           barbican:
             enabled: true
 
+Adding cron-job
+---------------
+
+.. code-block:: yaml
+
+    glance:
+      server:
+        cron:
+          cache_pruner:
+            special_period: '@daily'
+          cache_cleaner:
+            hour: '5'
+            minute: '30'
+            daymonth: '*/2'
+
+
+Image cache settings
+--------------------
+
+.. code-block:: yaml
+
+    glance:
+      server:
+        image_cache:
+          max_size: 10737418240
+          stall_time: 86400
+          directory: '/var/lib/glance/image-cache/'
+
 
 Client role
 -----------