Update the Simplified Provisioning documentation to include a detailed description

[pcdubs]

Currently the simplified-provisioning section of our documentation is missing a description of the simplified provisioning, add one.

Docs:
https://docs.fedoraproject.org/en-US/iot/booting-the-simplified-provisioner/

F40 change:
https://fedoraproject.org/wiki/Changes/IoTSimplifiedProvisioning

[CBeez23]

Please review and merge or leave revision requests: https://github.com/fedora-iot/iot-docs/pull/111/changes