Add documentation

[Krolken]

THe documentation in the README should have some info on how to use the library.

There is doumentation in the cli via nbiot --help

 nbiot --help
Usage: nbiot [OPTIONS] COMMAND [ARGS]...

  This is a NB IoT Scanner software built by Palmlund Wahlgren Innovative
  Technology AB in Sweden for use in finding problems and evaluating network
  coverage in smart meter rollouts.

Options:
  -p, --port TEXT                 Register the serial port to use
  --roaming / --home-network      Indicate if the MNO is using home network or
                                  roaming status
  --mno TEXT                      ID of MNO (Mobile Network Operator) ex.
                                  Telia Sweden = 24001
  -l, --loglevel [DEBUG|INFO|WARNING]
                                  Choose loglevel
  --psm                           If Power Save Mode should be used.
  --apn TEXT                      choose apn
  --help                          Show this message and exit.

Commands:
  connect  The scan command enables you to connect and get information of...
  ping
  reboot
  send
  stats

But there should be more in the repo