Reference 'How to Run' somewhere

It would be nice to have a 'How To Run' Section in somekind of README.

Especially since you have to set a higher `ulimit` to get to run the container.

Something along the lines of
```
docker run -it --ulimit nofile=122880:122880 -m 3G --rm rumbledb/rumble --shell yes
```
would be nice.