docs: update README and index with WebSocket support and acknowledgments

[ryanwclark1]

Summary

This pull request updates the README.md and docs/index.md files to refer to the new WebSocket support that was introduced and documented in commit 95aebc3. Specifically:

• Adds references to WebSockets support in the project description and features list.
• Documents the httpx2[ws] install extra.
• Adds wsproto under optional dependencies.
• Acknowledges François Voron and the httpx-ws package as the foundation for the native WebSocket implementation, aligning with the credit given in docs/websockets.md.

Checklist

• I understand that this PR may be closed in case there was no previous discussion. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change. (N/A: Documentation-only change, so no tests are needed.)
• I've updated the documentation accordingly.

[codspeed-hq]

Merging this PR will not alter performance

✅ 15 untouched benchmarks
⏩ 7 skipped benchmarks¹

---

_{Comparing ryanwclark1:docs/websocket-readme (ec54bd1) with main (c4e73cf)}

Footnotes

1. 7 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[cubic-dev-ai]

No issues found across 2 files

_{Re-trigger cubic}