Create a "contributing" section in the readme

[roll]

Overview

It will be great to have a contributing section in the readme containing a list of commands required to get started to work on the project. E.g. in Python it contains commands needed to setup virtual environments, install dependencies and run tests.

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That worked for me:

# install jabba and maven2
$ cd tableschema-java
$ jabba install 1.8
$ jabba use 1.8
$ mvn install -DskipTests=true -Dmaven.javadoc.skip=true -B -V
$ mvn test -B

[georgeslabreche]

@roll @pwalsh, should be good now.