Generate readme for ml_engine/online_prediction/README.md

[elibixby]

Docs link is available in the README.

[engelke]

Should this be tracked by an internal bug instead of here?

[engelke]

The creator of the code should update the README or assign someone familiar with it to do so.

[nnegrey]

Most of these samples have been migrated to https://github.com/GoogleCloudPlatform/cloudml-samples/
Closing