docs: opt entity doc

[luzhuang]

Please check if the PR fulfills these requirements

• [x] The commit message follows our guidelines
• [ ] Tests for the changes have been added (for bug fixes / features)
• [ ] Docs have been added / updated (for bug fixes / features)

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

link: https://github.com/galacean/engine/issues/2318

Summary by CodeRabbit

• Documentation
  • Enhanced clarity and detail of editing capabilities for entities, specifying multiple editable attributes (Name, IsActive, Transform, Layer).
  • Added explanations on layer management and its applications in clipping masks and ray detection.
  • Introduced new subsections on locating entities in the scene by name and path.