[ASK] Add info to top-level README

[chenhuims]

Description

• Add a Content table to list the examples in the repo (see https://github.com/microsoft/nlp-recipes/blob/master/README.md)
• Add an Azure Machine Learning Service section to summarize the dependency on Azure ML service (see https://github.com/microsoft/nlp-recipes/blob/master/README.md)
• Add a References section to link to other repo (e.g. https://github.com/Azure/DeepLearningForTimeSeriesForecasting,
  https://github.com/Azure/cortana-intelligence-price-optimization)

In which platform does it happen?

How do we replicate the issue?

Expected behavior (i.e. solution)

Other Comments

[chenhuims]

Added Content table and References. Will see if it's necessary to add a section for Azure Machine Learning Services based on user feedbacks.