Update doc image

README.md

@@ -5,21 +5,10 @@
 NNI (Neural Network Intelligence) is a toolkit to help users run automated machine learning experiments. 
 The tool dispatches and runs trial jobs that generated by tuning algorithms to search the best neural architecture and/or hyper-parameters in different environments (e.g. local machine, remote servers and cloud).
 
-```
-            AutoML experiment                                 Training Services
-┌────────┐        ┌────────────────────────┐                  ┌────────────────┐
-│ nnictl │ ─────> │  nni_manager           │                  │ Local Machine  │
-└────────┘        │    sdk/tuner           │                  └────────────────┘
-                  │      hyperopt_tuner    │
-                  │      evolution_tuner   │    trial jobs    ┌────────────────┐
-                  │      ...               │     ────────>    │ Remote Servers │          
-                  ├────────────────────────┤                  └────────────────┘
-                  │  trial job source code │                  
-                  │    sdk/annotation      │                  ┌────────────────┐
-                  ├────────────────────────┤                  │ Yarn,K8s,      │
-                  │  nni_board             │                  │ ...            │
-                  └────────────────────────┘                  └────────────────┘
-```
+<p align="center">
+<img src="./docs/nni_overview.png" alt="drawing" width="800"/>
+</p>
+
 ## **Who should consider using NNI**
 * You want to try different AutoML algorithms for your training code (model) at local
 * You want to run AutoML trial jobs in different environments to speed up search (e.g. remote servers and cloud)