Missing instructions for using gdocs_reader.py

[ChrisTimperley]

It would be nice if we could add an entry on how to use gdocs_reader.py to scripts/README.md. In particular, it would be useful to know how users should obtain a token.pickle or credentials.json file.

[hsd-dev]

BTW the script will not work till the "porting" is complete: https://github.com/ChrisTimperley/ese-robust/issues/30#issuecomment-884194575