docs: improve quickstart

[lnielsen]

Docs: http://invenio.readthedocs.io/en/latest/quickstart.html

Visually improve the section to make it easier for newcomers to digest. E.g. I find the part from Create a record to seem quite heavy

[dinosk]

Note: The ./scripts/setup fails because in invenio shell, app.config['CACHE_REDIS_URL'] is set to localhost:6379 but it should be <docker-machine ip>:6379.

This is solved by enabling Port Forwarding on my VirtualBox Manager, probably doesn't need to be mentioned.