document new buffer hack

doc/index.html

@@ -40,10 +40,21 @@ too.
 
 <p>Next is the path to the login shell.  The default Android shell is
 <tt>/system/bin/sh</tt>, but you may prefer to use the one that comes with
-busybox or whatever.</p>
-
-<p>Finally is the path for the home directory, which also defaults to
-<tt>/sdcard/ssh</tt>.  This is where your ssh session starts out, and is
+busybox or whatever.  If you set it to the su binary (i.e.,
+<tt>/system/xbin/su</tt>), then scp, sftp, and
+rsync will run as root and should be able to access files
+outside of the sdcard.</p>
+
+<p>A bug in SuperSU interacts with an infelicity in rsync to cause an
+occasional deadlock.  This is a real pain because I use SuperSU+rsync 
+for system-wide backups, which will always eventually trigger the
+deadlock.  To work around this, there is a "Buffer hack" option that
+should be enabled if you use rsync with SuperSU.  It adds a miniscule
+overhead to rsync, but isn't harmful even if you aren't using
+SuperSU.</p>
+
+<p>Finally, there is the path for the home directory, which also defaults
+to <tt>/sdcard/ssh</tt>.  This is where your ssh session starts out, and is
 where <tt>.profile</tt> will be found if it is present.</p>
 
 <p>There is also a place where you can put commandline options for