DOCS-471 adding note about ulimit

Author: Sam Kleinman

draft/administration/ulimit.txt

@@ -122,6 +122,11 @@ Substitute the ``-n`` option for any possible value in the output of
    ``/proc`` file system to see the current limitations on a running
    process.
 
+   Depending on your system's configuration, and default settings, any
+   change to system limits made using ``ulimit`` may revert following
+   system a system restart. Check your distribution and operating
+   system documentation for more information.
+
 ``/proc`` File System
 ~~~~~~~~~~~~~~~~~~~~~