Document denoland/deno#31890 TTY stream fix summary

[Copilot]

denoland/deno#31890 addresses crashes in Node compatibility when TTY streams are created with file descriptors beyond stdin/stdout/stderr. This PR adds a concise repository summary so consumers can quickly understand the scope and resolution.

• Documentation update
  • Added a dedicated README section that captures the issue context, the op-level fix, and the JS TTYStream behavior.

Example excerpt:

## Upstream Issue Summary (denoland/deno#31890)

- Deno previously restricted TTY streams to file descriptors 0-2, which caused
  Node compatibility crashes when packages created TTY streams on other fds.
- The fix adds an op to open TTY resources from any valid terminal fd by safely
  duplicating the descriptor and validating it is a TTY.
- A JavaScript TTYStream wrapper now handles arbitrary fds, while ReadStream and
  WriteStream keep the 0-2 fast paths for stdin/stdout/stderr.

Original prompt

understand denoland#31890 and summerize

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