Windows installation with poetry

[tjbarnum13]

Two issues arise with installation of PySpecTools on Windows with the new poetry method. Recommend updating installation instructions in README as a patch.

1. If installing in a virtual environment, poetry will default create its own virtual environment, which messes up the installation. This can be fixed by setting: poetry config virtualenvs.in-project false and poetry config virtualenvs.create false to prevent creation of any new virtual environments.
2. There is a known issue with the current release of poetry that results in "ValueError *.whl not found" (see ValueError, whl in cache does not exist when running poetry install again python-poetry/poetry#4163). Several workarounds have been found and are detailed in this thread. The workaround, which I have found works consistently across different versions of poetry and Windows, is to navigate to C:\Users\user\AppData\Local\pypoetry\Cache and delete everything in this folder. Then you can run poetry install successfully.