Expand on direnv section

The direnv section simply refers the reader to direnv.net for Linux installation instructions (by the the site is not linked on the page). Since there are different ways to get direnv working depending on if you're using pyenv, virtualenv, or virtualenvwrapper, it seems reasonable to direct them to the site. However, after struggling with this myself I found the instructions not straightforward, especially for a new user.
Since the direnv section directly follows the virtualenvwrapper section, I suggest updating with the following instructions to get direnv working with virtualenvwrapper:

1. Add the following to ~/.config/direnv/direnvrc

layout_virtualenv {
    local venv_path="$1"
    source ${venv_path}/bin/activate
}
layout_virtualenvwrapper {
    local venv_path="${WORKON_HOME}/$1"
    layout_virtualenv $venv_path
}

2. Add the following to an .envrc file in the root directory of your project
   layout virtualenvwrapper _name_of_virtual_environment_

Now, the virtual environment will activate when you enter the project directory and deactivate when you leave.

定位紧接在 virtualenvwrapper 部分之后的 direnv 部分，并检查周围的文档如何链接到外部安装指南。添加 direnv.net 链接和提供的 virtualenvwrapper 设置步骤，然后验证渲染后的指南是否清楚地说明了进入和离开项目目录时的激活过程。