Update README.md

As per the python documentation "The xmlrpclib module has been renamed to xmlrpc.client in Python 3"
So I guess this script uses the version 3 of python which need to be installed properly to avoid problems.
Update README.md

Fix the error returned by the cron job (/bin/sh: can't find gandyn.py)
Update README.md

The script won't run from cron job if the execute permission is not set on gandyn.py
Merge pull request #7 from david-soyez/master

Update README.md