Describe how to update `get_poetry.py`

[tomuben]

Summary

Describe how to update get_poetry.py in developer guide.

Details

In #553 we started to use a local copy of get_poetry.py, downloaded from https://install.python-poetry.org/. We should describe in the developer guide how to update the file.

Background & Context

References

Task(s)

• Add section in developer guide about how to update get_poetry.py