Add alternative non-docker install

[anaivebird]

It seems that the dependency is not so much:

1. ninja (apt install ninja-build,)
2. intel MTK (pip install mtk) (which is actually not needed if using GPU inference only, but it lays on build dependency).
3. onmt (pip install OpenNMT-py) (if you want to pass unitest)

So may be we could provide a non-docker install methods which is far more lightweight.

[feifeibear]

Hello, sorry for my late response. I assume MTK -> MKL. Please refer to the README.md of branch ppopp21_artifact_centos for installation without docker. https://github.com/Tencent/TurboTransformers/tree/ppopp21_artifact_centos

[feifeibear]

BTW, you can copy installation scripts from that branch to branch master. Or pull master to branch ppopp21_artifact_centos.