Add an FAQ entry about the sync client's sub-directory scan limit

As requested in #1067, this commit adds an entry to the FAQ to highlight
the fact that the sync client will never scan greater than 50
sub-directories.

doc/faq.rst

@@ -10,3 +10,11 @@ continually changes all files, unless you remove
 ``\HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\PropertySystem\PropertyHandlers``
 from the windows registry.
 See http://petersteier.wordpress.com/2011/10/22/windows-indexer-changes-modification-dates-of-eml-files/ for more information.
+
+Syncing breaks when attempting to sync deeper than 50 sub-directories, but the sync client does not report an error (RC=0)
+--------------------------------------------------------------------------------------------------------------------------
+
+The sync client has been intentionally limited to sync no deeper than
+fifty sub-directories, to help prevent memory problems. 
+Unfortunately, it, *currently*, does not report an error when this occurs. 
+However, a UI notification is planned for a future release of ownCloud.