Python install command is incorrect

The install command assumes that the client is in the root of the repo. This needs to be updated to point to the python-client sub-directory.

```bash
pip install -e "git+https://github.com/libretime/api-client.git#egg=libretime_client&subdirectory=python-client"
```

https://github.com/libretime/api-client/blob/main/python-client/README.md?plain=1#L20