doc: python bindings howto
doc: python bindings howto

* Made the changes suggested by Jakub Wilk on gnupg-devel.
* Still need to make the far more comprehensive changes suggested by Justus.

gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme