新安装的Unity，选择代码IDE的地方无法自动识别visual studio了。安装微软官网以下提示解决：
Add a version of Visual Studio that is not listed
It's possible to select other versions of Visual Studio that are unlisted and installed in a custom directory.
- Select Browse... from the dropdown list.
- Navigate to the Common7/IDE directory inside your Visual Studio installation directory and select devenv.exe. Then, click Open.
- For Unity 2019 and older only, confirm that the Editor Attaching checkbox is selected.
- Close the Preferences dialog to complete the configuration process.
