update README

[laDok8]

No description provided.

[randriu]

I'm not sure if I like the idea of making paynt.py executable. I think a more standard practice is to use the included setup.py to add paynt to your python environment -- I personally do not use it, so I don't know whether it still works.

Apart from this, your other changes that make the README up-to-date are welcome.

[laDok8]

agreed, I would probably mention alias paynt = python3 <PAYNT_DIR>/paynt. Imo making README easier to read and making it available to use from any dir

[randriu]

I simplified the alias presentation a bit and moved it to the end of the section to preserve the flow of the README.