PyManager shebangs do not document auto-install behaviour

[zooba]

At https://docs.python.org/dev/using/windows.html#shebang-lines it should mention that if a shebang is included but not installed, a matching runtime will be installed automatically (unless configured off).

Linked PRs

• gh-133928: Improvements to using/windows.rst #133952
• [3.14] gh-133928: Improvements to using/windows.rst (GH-133952) #133977