publish instructions for how to run tests

[neonstalwart]

a node idiom (and hence a de facto package.json idiom) is that npm install should install all dependencies and then npm test would run the tests. currently when i try to run npm install it fails because dstore is not published to npm.

i'm really not concerned about what the exact method is to install the dependencies and run the tests but having a simple way of doing this helps with continuous integration and gives contributors a simple way to test their contributions.

if i can know how to run the tests i'll open a PR with a .travis.yml to get CI working.