Add listener to run_ingest.sh to listen to file changes in sylinked directory

[misslivirose]

The current script only listens for modifications to the downloads folder, which means that if you manually add a file to a subdirectory in source_documents, it won't trigger the ingest script to run.

This isn't a huge issue, because it's going to pick it up in the next saved document anyway, but it might be good to have a flag to "listen" more intently to when new files are added, regardless of how they make their way into the cache.