Docs: Partners: Add JPS provisioning/cancelling doc

[ebinnion]

We currently send the following documentation to hosting partners when to explain the technical bits of provisioning plans via a PDF. This works, but has a few issues:

• We have to manually send this file
• If we update the documentation, we then have to send the file again
• If we have update, even if we send the updated documentation, the host may continue to use the outdated documentation

Putting this documentation into the Jetpack repository itself allows partners to easily find the documentation and to view the most up-to-date version of the documentation.

CHangelog etnry

• We improved the documentation for partners so they're now able to get them right on the Jetpack's Github repository under the docs/partners directory.