tar: Removing leading `/' from member names

[Alan Young]

I've got a cron job running a backup every night.  It's a shell script
that looks like this:

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#!/bin/bash

cd /backup

tar -czf webstoresDoc.tgz -C / /home/www/docroot/webstores
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It works fine, but I keep getting the following email from the cron process:

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tar: Removing leading `/' from member names
tar: Removing leading `/' from member names
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Originally, the '-C /' wasn't there, but after some googling I found
this switch which is supposed to--among other things--get rid of this
warning.

I've tried 'czf' instead of '-czf' and '-C' instead of '-C /' in all
the combinations I can think of.

I'd prefer to avoid piping STDERR to /dev/null because I want to be
notified if something goes wrong, but I don't want my inbox cluttered
with useless messages either.

Any pointers?
-- 
Alan