serve: Fix corner cases where the pipeline doesn't run correctly. * When `chef serve` is run before the `assets` folder is created, monitor that folder suddenly appearing and rebuild the pipeline. * Do the same when the `config.yml` file has changed.

--exclude=build
--exclude=dist
--exclude=docs/_cache
--exclude=docs/_counter
--exclude=docs/bower_components
--exclude=docs/node_modules
--exclude=docs/raw
--exclude=*.egg-info
--exclude=__pycache__
--exclude=__tmpfs__