polished README.md 

Polished README.md towards making a release that may accompany a potential data deposition on zenodo.org. 
* Included the citation of the publication.
* Wrote a few words about the method
* Commented out the stuff abouth the Qt GUI.

Also, added datamaker.py to this repository to avoid the extra dependency when running the regNMF example notebook.

Finally, the regNMF notebook contained a few bugs which I fixed. I also added some improvements and a couple of TODO notes. The TODO notes mainly refer to fixing deprecation warnings and adding progress bars where the computation tends to take long. I will approach these next week, hopefully.