Adding a new installation method to the README

Hi, we have implemented a lightweight [package manager using shell and awk](https://www.x-cmd.com/pkg/).
It helps you download gitui 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 gitui README?
[The installation method for the x command](https://www.x-cmd.com/start/)

install gitui:
```bash
x env use gitui
```
[gitui demo](https://www.x-cmd.com/pkg/gitui): x-cmd recorded a demo and article for gitui

I apologize in advance if it's not appropriate to raise this topic using a GitHub issue.
Looking forward to your reply :) !