BERT README.md contains no documentation, only a redirect

[kredd2506]

Description

The BERT model README at models/official/bert/README.md contains only a single line:

See https://github.com/google-research/bert/blob/master/README.md

Problem

• No setup instructions, usage examples, or TPU-specific guidance in this repo
• Users landing on this directory have no context on how the BERT implementation here relates to or differs from the google-research/bert repo
• Other models in models/official/ (e.g., EfficientNet, Mask R-CNN) have detailed READMEs with training commands, expected results, and configuration options

Suggested Fix

Add a README that covers at minimum:

• What this BERT implementation provides (and how it differs from google-research/bert)
• How to run BERT training/fine-tuning on Cloud TPU
• Supported configurations and expected performance
• Link to the upstream repo for additional context