ragleap-vectorstores v0.3.1

Docs/metadata-only patch.

Fixed

• README's Usage section was missing a RedisBackend example (only Chroma/LanceDB were shown).
• pyproject.toml keywords expanded with per-backend terms (chroma, chromadb, lancedb, redis, redisearch, embeddings, similarity-search) for PyPI discoverability.

No code changes; all 40 tests still passing.