To enable uploading and processing of Plaso storage files, there are a couple of things to do.
Install Plaso
NOTE: Due to changes in the format of the Plaso storage file you need to run the latest version of Plaso (>=1.5.0).
Following the official Plaso documentation: https://plaso.readthedocs.io/en/latest/sources/user/Ubuntu-Packaged-Release.html
$ sudo add-apt-repository universe
$ sudo add-apt-repository ppa:gift/stable
$ sudo apt-get update
$ sudo apt-get install plaso-tools
Install Redis
$ sudo apt-get install redis-server
Configure Timesketch (/etc/timesketch/timesketch.conf)
UPLOAD_ENABLED = True
UPLOAD_FOLDER = u'/path/to/where/timesketch/can/write/files'
CELERY_BROKER_URL='redis://127.0.0.1:6379',
CELERY_RESULT_BACKEND='redis://127.0.0.1:6379'
Run a Celery worker process
$ celery -A timesketch.lib.tasks worker --loglevel=info
Read on how to run the Celery worker in the background over at the official Celery documentation.