docs: fix README grammar and typo

[cuiyingd]

Purpose

Fix two small documentation issues in the project README: a grammatical wording that made "inference" read like a verb, and a typo in the FAQ heading.

Change Summary

• Modified README.md:
  • Reworded: "reproduce, fine-tune, and inference..." → "reproduce, fine-tune, and run inference on..."
  • Fixed typo: "Coverting RLDS/LeRobot to Dexdata" → "Converting RLDS/LeRobot to Dexdata"

Benchmark Evidence

• Not applicable (documentation-only change).

Dependencies

None

Environment

Not applicable (docs change)

✔️ Review Checklist (must all be checked)

• No breaking changes to core interfaces (VLA API / Dexdata) — docs only.
• No redundant implementation (checked existing modules first) — no code added.
• Code follows existing design link — not applicable; docs-only change.
• Local validation completed with commands + expected output — git show confirms the edits.
• Benchmark evaluation completed and attached — N/A (docs-only).
• No regressions observed — docs-only.
• No new dependencies or all new dependencies listed — None.
• Merges cleanly on current main and builds successfully — should merge cleanly; no build impact.

[cuiyingd]

@hbzfeng @yuzhms can you please review?