default license more adapted to data + fix init in CLI + edit in README

I am by no means an expert in licenses but [this](http://opendatacommons.org/faq/licenses/#Why_Not_Use_a_Creative_Commons_or_FreeOpen_Source_Software_License_for_Databases) seems (somewhat) convincing.
I checked the standard SPDX ID [here](https://spdx.org/licenses/PDDL-1.0).

[CC0-1.0](http://spdx.org/licenses/CC0-1.0) could work too.