Add reference to paper to README #72

Now that we have a paper to appear, we should add a reference for people to cite if they use nameCollector in their research.

If using nameCollector as part of published research, please cite:
Sipahioglu, J.A., Behler, J.A.C., Testa, S., Al-Ramadan, A., Decker, M.J., Collard, M.L., Maletic, J.I., (2026) “nameCollector: Extracting Source Code Identifiers Along with their Types and Context”, in the Proceedings of 42nd IEEE International Conference on Software Maintenance & Evolution (ICSME), Tool Demonstrations Track, Benevento, Italy, Sept 14 - 18, 5 pages.