Add basic development and deployment info to README

[effa]

See e.g. https://github.com/adaptive-learning/flocs for inspiration

[effa]

Also include somewhere information about concurrent development of web and core/fvc (i.e. how to use local (unreleased) version of another package):

Python:

• https://pip.pypa.io/en/latest/reference/pip_install/#editable-installs
• pip install -e ../flocs-core
• problem: be careful not to include local version into requirements.txt (which could easily happen by pip freeze > requirements.txt)

JS:

• npm link ?
• alternative (less convenient, needs reinstall on change of fvc): npm install ../../flocs-visual-components/