Document Windows setup?

[PeterJCLaw]

Many Windows installs need to specify explicitly to Webots where the Python install is.
Presumably this is those where python.exe isn't on %PATH%.

One possible error to watch for is accidentally setting the path to the directory rather than including the filename too.

[WillB97]

Indeed the option to add python to %PATH% is not selected by default in the installer. In this can they will need to give Webots the absolute path which is normally C:\Users\<USERNAME>\AppData\Local\Programs\Python\Python37\python.exe