Python version specified in Download and install page

The Download and Install page states that at least Python 3.8 or newer is required to install Emscripten. That might be true - the installation succeeds with Python version 3.9 - but after installation "emcc --version" crashes with a syntax error in a Python script. Installing Python version 3.14 resolved the issue. It might be recommendable to specify on this page the Python version actually required to run emcc.

从 repository 的“Download and Install”页面开始，在文档所述的 Python 版本下运行 emcc --version，以复现报告的行为。确认运行 emcc 所需的 Python 版本，然后更新该页面，使安装和运行时要求准确无误。

由索引模型根据 Issue 内容生成。