Document how to do image extraction in processing container

[lwrubel]

JWAT tools and warctools are provided in the processing container. Investigate which can be used to extract images. Document the steps for doing this.

[justinlittman]

Also look at https://github.com/chfoo/warcat. May want to add as an available tool.

[kerchner]

This can be addressed after the issue of heretrix web harvesting failing is addressed

[justinlittman]

See also https://github.com/jaygattuso/WARC_dumper.