place the initial credentials.json file into the local working directory
use the get_gmail_credentials() function to trigger the login prompt
sign in with the google account that you want to use - a token.json should be created
if being used on a automated system for emailing (i.e. windows task scheduler, linux chronjobs) the credentials should be refreshed before expiration (i.e. run get_gmail_credentials() once a day)
make calls to the send_message() function for automated emailing