Troubleshoot + Update README developer documentation

[katiestahl]

I was following the instructions in the readme to update the data and schemas for #126 , but I kept running into issues. It would be nice to have other developers also test out the readme instructions to find any potential issues and add troubleshooting or explicitly clear instructions for development setup to the readme.

We should include the following information in the readme developer documentation:

• detailed setup instructions (ie; should they have a venv running before doing anything? should they be able to run pip install -e . with no issues? should they run that command or make install? etc.)
• prerequisites (ie; should poetry be installed already? should we add a requirements file or make command to do this for them?)
• cloning instructions (this may seem a bit overkill, but since the project dependencies are managed by poetry, which expects specific package and directory names, we should make it clear that the developer should not have a custom local name for the project)