Add a simple script for running rsync_tmbackup.sh from cron.

So, rsync_tmbackup.sh is really nice, but it won't run itself!

Probably everybody who uses rsync_tmbackup.sh runs it from cron or something similar, so here is a nice simple little script that people can use, so that each new user doesn't have to create this from scratch themselves.

So far it supports Ubuntu and Fedora, shouldn't be hard to add Mac if you tell me how Mac mounts it's removable drives. What I like about this is that it's only 6 lines of code, it scans for all marked backup destinations, can be used by any user of the system, and allows users to specify their excludes without having to modify this script. 

And I tested, it works with spaces in filenames ;-)