demo: add scripts for cleaning leftover files

The demo expects its storage directory to be clean at start, otherwise undefined behavior will occur.

demo/README.rst

+To run the demo, make sure all the dependencies are installed and run `./cleanfull.sh` and then `./demo 8000` (or any port).
+

demo/clean.sh

+#!/usr/bin/env bash
+
+for b in $(sudo ip l | grep -Po 'NETNS\w\w[\d\-a-f]+'); do sudo ip l del $b; done
+pkill screen
+killall python
+killall python3
+find . -name '*.db' -delete
+find . -name '*.crt' -delete

demo/cleanfull.sh

+./clean.sh; find . -name '*.crt' -delete; find . -name '*.db' -delete; find . -name '*.log' -delete