Update src/chapter_03_publishing_and_distribution/00_publishing_anonymously.md

Added reference to ExifTool for meta-data removal.
Website: http://owl.phy.queensu.ca/~phil/exiftool/
Debian Package: http://packages.debian.org/sid/libimage-exiftool-perl
(Debian) install with: $ apt-get install libimage-exiftool-perl
Basic Usage
Check the current meta data on a file with: $ exiftool foobar.jpg
Remove all exif data from jpegs in a local directory): $ exiftool -all= *.jpg
Remember to manually check the files that just had their meta data removed before deleting the backups created with:
rm *.jpg_original