Adding a new installation method to the README

Hi, we have implemented a lightweight package manager using shell and awk.
It helps you download dua release packages from the internet and extract them into a unified directory for management, without requiring root permissions.
I mean, can the installation method provided by x-cmd be added to the dua README?The installation method for the x command
```
x env use dua
```

Looking forward to your reply :) !

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