README.md

Practice for github and Docker

1. Send first pull request here Done (Y/N): Y

1.1. Update this new sentence to your personal repo. Done (Y/N):

2. Push a example cpp file and a Makefile to complile it, it must be compilable Done (Y/N):
3. Create a Dockerfile which to auto download this repo and auto compile the cpp file
   Done (Y/N):