requirements.txt and README may cause build error

[virgiling]

The second way to build SparTA in Get Start part in README is wrong.
The correct way to build it from source code may be this:

git clone https://github.com/microsoft/SparTA.git
cd SparTA
pip install -r requirements.txt
python setup.py install

and there is a bug in requirements.txt, it is missing a package ninjia.
If ninjia is not installed, it will cause an undefined symbol: xxxxxx.so xxxxx error