Download potion from here by clicking on the ‘Download’ button. Then unzip potion, cd to that directory, and run:
$ make
There should be no errors and you should see a welcome message at the end of the output. If anything goes wrong, report it here.
You now have a ‘potion’ binary in the directory. Optionally, to test it, run:
$ make test
~
$ ./potion the_file_to_run.pn