README repeats backend prerequisites and links to a removed miden-debug branch

The README currently has two identical `Backend prerequisites` sections in the debugging docs.

Both copies also link `0xMiden/miden-debug` to:

```text
https://github.com/0xMiden/miden-debug/tree/feature/vscode-dap-plugin
```

That branch now returns 404. The `miden-debug-engine` changelog in the current `miden-debug` repo shows the relevant DAP attach support has shipped, so the README should not send users to the removed feature branch anymore.

A small docs fix would remove the duplicated prerequisite block and update the `miden-debug` prerequisite wording/link to point at the released/current debugger path instead of the stale branch.

The issue is about the README file. Open the README.md in the repository root, find the 'Backend prerequisites' sections in the debugging documentation, and remove the duplicate. Update the link for 'miden-debug' from the stale feature branch to the main repository or a current release path. Verify the changes by previewing the README.

索引モデルが issue の本文から書いたものです。