[lldb][docs] Mention "Python Install Manager" in Windows build instructions (#188728)
It was reported to us that this new install manager does not, and
apparently will not, have an option to install a debug Python. Which we
must have to be able to build lldb in debug mode on Windows.
(because the debug C runtime has a different ABI so everything in the
build must use only that version)
https://discourse.llvm.org/t/pythonx-d-lib-build-requirement/90285/1
Developers will have to use the "Windows installer", or build thier own,
so I've linked to Python's documentation for that.