Change commands in PPH Django wiki

[lukpueh]

(1) In the third verbatim block in getting the sources one has to copy django_pph into the testapp dir using the command:

$ cp -r PolyPasswordHasher-Django-master/django_pph/ my_django_project/

On OS X the trailing slash after django_pph makes that it copies the contents of django_pph to my_django_project instead of the directory.

(2) In Creating User Accounts the createsuperuser management command lists an optional [username] argument. Which it actually does not accept (at least not in django 1.10.4).