add Dockerfile to easily build elasticsearch into a runnable linux container

It would be nice to have a Dockerfile for this project, to be able to start an ElasticSearch container easily.

1) Instal docker `http://docker.io`
2) Download the Dockerfile `wget https://raw.github.com/vieux/elasticsearch/dockerfile/Dockerfile`
3) Build the container using the Dockerfile `docker build - < Dockerfile`
4) Start ElasticSearch with `docker run <imageid>`

That's it!