Improve README and add comments for transfer learning examples

[NA-V10]

Summary

Improved documentation for transfer learning examples and added inline comments for clarity.

Changes

• Rewrote README with detailed explanations of each transfer learning strategy
• Added comments to EditLastLayerOthersFrozen.java
• Added comments to EditAtBottleneckOthersFrozen.java
• Added comments to FineTuneFromBlockFour.java
• Clarified folder structure and usage examples

Why

Transfer learning is one of the most important DL4J use cases. This PR improves clarity and makes the advanced examples easier to understand for learners.