Improve main README with repo purpose and structure (#228)

* Update main README with purpose and repo structure

* Improved description of what is in the repo

* Removed training/edge and added bare metal

* More wording changes

README.md

@@ -1,7 +1,34 @@
 # Model Zoo for Intel® Architecture
 
-This repository contains a number of models optimized by Intel to run machine
-learning workloads on Intel® Xeon® Scalable processors. For information on
-how to run key benchmarks, see the [README](/benchmarks)
-in the benchmarks folder. How-tos and tutorials can be found in the [docs](/docs) folder.
+This repository contains **links to pre-trained models, benchmarking scripts, best practices, and step-by-step tutorials** for many popular open-source machine learning models optimized by Intel to run on Intel® Xeon® Scalable processors. 
 
+## Purpose of the Model Zoo
+
+  - Demonstrate the AI workloads and deep learning models Intel has optimized and validated to run fast on Intel hardware
+  - Show how to efficiently execute, train, and deploy Intel-optimized models
+  - Make it easy to benchmark model performance on Intel hardware
+  - Make it easy to get started running Intel-optimized models on Intel hardware in the cloud or on bare metal
+
+## How to Use the Model Zoo
+
+### Getting Started
+- If you know what model you are interested in, or if you want to see a full list of models in the Model Zoo, start **[here](/benchmarks)**.
+- For framework best practice guides, and step-by-step tutorials for some models in the Model Zoo, start **[here](/docs)**.
+
+### Directory Structure
+The Model Zoo is divided into four main directories:
+- **[benchmarks](/benchmarks)**: Look here for benchmarking scripts and complete instructions on downloading and benchmarking each Intel-optimized pre-trained model.
+- **[docs](/docs)**: General best practices and detailed tutorials for a selection of models and frameworks can be found in this part of the repo. 
+- **[models](/models)**: This directory contains optimized model code that has not yet been upstreamed to its respective official repository, such as dataset processing routines. 
+  There are no user-friendly READMEs in this directory, but many supporting modules used for benchmarking are here.
+- **[tests](/tests)**: Look here for unit tests and information on how to run them. 
+
+The benchmarks, models, and docs folders share a common structure. Each model (or document) is organized first by *use case* and then by *framework*. 
+Inside the model-specific directory, there may be further nesting subdirectories for inference vs. training and FP32 vs. Int8 precision. 
+We hope this structure is intuitive and helps you find what you are looking for; when in doubt, consult the section's main README. 
+
+![Repo Structure](repo_structure.png)
+
+## How to Contribute
+
+Coming soon