add instruction to create DB and start project with testing DB.

README.md

+This project delivers some python code for management of elements with system label within a Flask application.
+
+For testing purpose, a Flask demonstration web site is provided, 
+to create testing database. Execute the following shell commands from project's root.
+```
+mkdir instance
+python3 -m venv venv
+source venv/bin/activate
+pip install -r requirements.txt
+python3 -c 'from models import db;db.create_all()'
+mv test.db voiture.db ou codingpool.db
+sqlite3 voiture.db '.read data_voiture.sql'
+mv voiture.db instance/
+```
+
+to be excuted with the help of Docker. You can move to the `docker`  subdirectory and read the local `READ.md` for a detailed description of the provided utility scripts. For the impatient users, the recipe to start the demo wen site is :
+
+```
+cd docker
+./build_dev.sh
+./run_dev.sh
+```
+