Update docs for VectorCypherRetriever

[willtai]

Description

Update VectorCypherRetriever to improve its usability.

Type of Change

• [ ] New feature
• [ ] Bug fix
• [ ] Breaking change
• [x] Documentation update
• [ ] Project configuration change

Complexity

Low

How Has This Been Tested?

• [ ] Unit tests
• [ ] E2E tests
• [x] Manual tests

Checklist

The following requirements should have been met (depending on the changes in the branch):

• [x] Documentation has been updated
• [ ] Unit tests have been updated
• [ ] E2E tests have been updated
• [ ] Examples have been updated
• [ ] New files have copyright header
• [ ] CLA (https://neo4j.com/developer/cla/) has been signed
• [ ] CHANGELOG.md updated if appropriate