optional geo dependencies, no documentation

[odscjen]

As per this changelog entry the WKT support is now optional rather than default but all you get when converting geodata is the following warning message

UserWarning: Install flattentool's optional geo dependencies to use geo features

But there's nothing in the flatten-tool documentation that I could see that says how to do this.

This came about when running manage.py pre-commit as part of OFDS development.

[jpmckinney]

The warning can add, e.g. ..., for example: pip install flattentool[geo]