Make the docs a bit more user friendly [#70840170]

- I've tried to break this down into sections that explain the files a bit more explicitly
- possible TODO: Move the google auth flow stuff to it's own section
- renamed the `generate_credentials` file to `generate-ga-credentials.py` as it is specific to google analytics
I think that's a bit misleading. If I read that I'd expect it to execute my-nice-time-function.