bsp: qemu-virt64-riscv: update README for booting with rootfs

[unicornx]

Now lwext4 is ready, and qemu-virt64-riscv smart can boot with rootfs.

Updated README to introduce this.

This patch also replace qemu-nographic.sh with run.sh, which has a more simple name and more robust to launch rootfs image binary.

TBD: qemu-nographic.bat is not touched, hope some guys from Windows can give a hand.

拉取/合并请求描述：(PR description)

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为什么提交这份PR (why to submit this PR)

你的解决方案是什么 (what is your solution)

请提供验证的bsp和config (provide the config and bsp)

• BSP:

• .config:

• action:

]

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• 本拉取/合并请求是一个草稿版本 This PR is for a code-review and is intended to get feedback
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代码质量 Code Quality：

我在这个拉取/合并请求中已经考虑了 As part of this pull request, I've considered the following:

• 已经仔细查看过代码改动的对比 Already check the difference between PR and old code
• 代码风格正确，包括缩进空格，命名及其他风格 Style guide is adhered to, including spacing, naming and other styles
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• 代码是高质量的 Code in this PR is of high quality
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[unicornx]

改了个 readme 为啥会导致 ci 失败？

[Rbb666]

@unicornx ci修复了