[Doc] Add PowerShell snippet in the installation instructions (web & scripts) to allow Windows users to modify `%PATH%` easier

• I have searched the issues of this repo and believe that this is not a duplicate.

Issue

https://python-poetry.org/docs/master/#installing-with-the-official-installer

Add Poetry to your PATH

The installer creates a poetry wrapper in a well-known, platform-specific directory:

• $HOME/.local/bin on Unix.
• %APPDATA%\Python\Scripts on Windows.

If this directory is not present in your $PATH, you can add it in order to invoke Poetry as poetry.

Alternatively, the full path to the poetry binary can always be used:

• $POETRY_HOME/bin/poetry if $POETRY_HOME is set.
• ~/Library/Application Support/pypoetry/bin/poetry on MacOS.
• ~/.local/share/pypoetry/bin/poetry on Linux/Unix.
• %APPDATA%\pypoetry\Scripts\poetry on Windows.

The following snippet is helpful and should be appended in the document for Windows users:

if (-not (Get-Command poetry -ErrorAction Ignore)) { [Environment]::SetEnvironmentVariable("Path", [Environment]::GetEnvironmentVariable("Path", "User") + ";$env:APPDATA\Python\Scripts", "User") }

or (for PowerShell 6+)

if (-not (Get-Command poetry -ErrorAction Ignore)) { echo 'if (-not (Get-Command poetry -ErrorAction Ignore)) { $env:Path += ";$env:APPDATA\Python\Scripts" }' | Out-File -Append $PROFILE }

P.S. The script provided by https://install.python-poetry.org also needs this fix.

リンク先の official-installer ドキュメントのセクションにあるインストール手順から始め、install.python-poetry.org が提供するインストールスクリプトを調べてください。標準の PowerShell と PowerShell 6+ における Windows PATH の案内を比較し、その後、ドキュメントとスクリプトの両方が報告された Windows セットアップのケースに対応していることを確認してください。