NEVER PUBLISH YOUR PRIVATE KEYS. That said, add public and private keys.

I'm doing this because this key is for a public development Mozilla
Persona IdP server.  I would like anyone else who wishes to contribute
to development and testing of this server to be capable of doing so,
without needing to clone Mozilla's repo, [0] install node, install NPM,
install a bunch more node crap, and then run some shitty node script
just to create an RSA key and format it in JSON.

[0]: https:// github . com /mozilla/browserid-certifier
Add docstring for provision.js signServerSideRestful().