doc: add information about NFS timeouts

closes #762

Author: satra

doc/users/debug.rst

@@ -58,4 +58,11 @@ performance issues.
    you will get a `ConcurrentLogHandler` error. Simply remove the pypeline.lock
    file in your home directory and continue.
 
+#. One many clusters with shared NFS mounts synchronization of files across 
+   clusters may not happen before the typical NFS cache timeouts. When using 
+   PBS/LSF/SGE/Condor plugins in such cases the workflow may crash because it 
+   cannot retrieve the node result. Setting the `job_finished_timeout` can help::
+   
+   workflow.config['execution']['job_finished_timeout'] = 65
+
 .. include:: ../links_names.txt