Make a better error message for no onshapepy credentials

[eak24]

When a user doesn't have credentials, we need to give them a better message

[lwanger]

I made some changes in my fork of onshapepy to improve getting credentials. Additionally, a package such as dotenv (https://github.com/theskumar/python-dotenv) should be used to allow credentials to be in a file the the users .env directory or set in an environment variable. This will help people keep access and secret keys secure.