Move data into src directory so it is accessible in installations
What's Changed
* Update installation & citation instructions by pheuer in https://github.com/pheuer/cr39py/pull/30
* Allow nbsphinx to actually run notebooks by pheuer in https://github.com/pheuer/cr39py/pull/31
**Full Changelog**: https://github.com/pheuer/cr39py/compare/v0.0.1...v0.0.2