Install NNI on Ubuntu

Installation

Dependencies
```
python >= 3.5
git
wget
```
python pip should also be correctly installed. You could use "python3 -m pip -v" to check in Linux.

Install NNI through pip

python3 -m pip install --user --upgrade nni

Install NNI through source code

git clone -b v0.3.4 https://github.com/Microsoft/nni.git
cd nni
source install.sh

Install NNI in docker image

You can also install NNI in a docker image. Please follow the instructions here to build NNI docker image. The NNI docker image can also be retrieved from Docker Hub through the command docker pull msranni/nni:latest.