rsync_tmbackup.sh: Improved usage and scripts output

[Tormen]

... in order for it to be more intuitive and self-explanatory (user friendly for new users).

• Added missing explanation about the exclude-from-file to make usage info (--help) self-contained to use for new users.
• Renamed LOG_FILE to RSYNC_LOG_FILE (as LOG_FILE might be confused with the log of the output of this script)
• Added the RSYNC_LOG_FILE path to the scripts output.
• Clarified the difference between a FULL and an INCREMENTAL backup in the scripts output.
• Forced a linebreak in script output (as line break was probable) to make things better readable.