Missing Windows step for installing coverage

In /coverage/ section 5.2.1.1
When installing coverage on Windows, the second command step can not be used:

source ../cpython-venv/bin/activate

Instead, there should probably be some mention of the proper step:

..\cpython-venv\Scripts\activate.bat

Which allows you to enter the virtual environment and continue with the instructions.

从 /coverage/ 文档的第 5.2.1.1 节开始，将现有的虚拟环境激活命令与 issue 中给出的 Windows 专用命令进行比较。更新说明以提及 Windows 激活步骤，然后确认相关的安装流程对于 Windows 读者来说仍然清晰。