Some docs on naming smmap vs smmap2

[AlanCoding]

In the links in your README.md, could you link to the PyPI page

https://pypi.org/project/smmap2/

I checked the page for just smmap, and that has not been updated in a long time, and I infer that smmap2 is what I want. It would just be good to have confirmation and a backlink so that people are sure of the correspondence when collecting licenses.