Update the README

[glemaitre]

The README needs an update to remove useless information.

TODO:

• move the tags on the top of the file;
• mention the needs for matplotlib for the examples;
• describe how to contribute with a development section;
• update the link to the citation -> as well in the documentation;
• remove the references section; -> we might keep this.
• remove that this work is in progress and that we want feedback.