Install instructions from git and example-query.sparql

This commit request explains the case of installation from a local git checkout.

It also adds an `example-query.sparql` to make it even easier to have a `hello world` working immediately.

Open for improvements :-) Maybe an `npm` commands can be added that will allow

```
$ ldf-client example-query.sparql
```
without needing the give the explicit ./bin/ path.