Windows install docs update

[wrh-dev]

• I have searched the issue tracker and believe that this is not a duplicate. (Possible regression of Installing pdm fails on Windows #2153)

Make sure you run commands with -v flag before pasting the output.

Steps to reproduce

Attempted to install in Windows based on the suggested command:

(Invoke-WebRequest -Uri https://pdm-project.org/install-pdm.py -UseBasicParsing).Content | python -

Actual behavior

An array of bytes is printed. pdm is not installed.

Expected behavior

pdm should have been installed.

Workaround

Explicitly encoding the content as a string allowed pdm to be installed.

[System.Text.Encoding]::UTF8.GetString((Invoke-WebRequest -Uri https://pdm-project.org/install-pdm.py).Content) | python -