docs: Added the Readme.md file for Nim interop test

[ItshMoh]

This pr includes the README.md file in the Nim interop tests. The README.md files includes details for running the tests.

fixes #1125

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[seetadev]

@ItshMoh : Hey Mohan — thanks for this PR and for taking the time to document the Nim interop tests 🙌
This is a useful and much-needed addition, especially for new contributors trying to run interop tests locally. The README is clear, scoped, and does a good job of lowering the entry barrier 👍

A couple of alignment notes and suggestions, just to make sure this lands in the right long-term place:

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📍 Repo alignment for interop documentation

Similar to the other interop work we discussed recently, interop tests and their documentation are gradually being centralized under:
👉 https://github.com/libp2p/test-plans

That repo is intended to be the canonical home for:

• Cross-implementation interop tests
• Test orchestration logic
• Contributor-facing docs on running and extending interop suites

Since this README is specifically about running Nim ↔ Python interop tests, it would be ideal for this documentation to eventually live alongside the Nim interop test plan in test-plans.

Suggested path forward:

• The content itself looks good and is worth keeping 👍

• We may want to either:

  • Move this README (or an adapted version of it) into test-plans, or
  • Follow up with a PR to mirror this documentation there, so contributors have a single place to look for interop guidance

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📦 Scope of py-libp2p

As a reminder for future interop-related PRs:

• py-libp2p → main should stay focused on core library code and shared utilities
• Interop logic and documentation is best kept in test-plans, where it can evolve across Go / Rust / JS / Nim consistently

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✅ On the PR itself

• Clear commit history ✔️
• Fixing linting and version mismatches along the way is appreciated
• README content is practical and contributor-friendly

Once we align on whether this should live here or be moved/mirrored into test-plans, I’m happy to see this merged or followed up accordingly.

Thanks again for improving the contributor experience — this kind of work really matters 👏

CCing @acul71 , @sumanjeet0012 and @dhuseby