Added more detailed documentation

For me bangsh balances simplicity and power in a great way. I wanted to learn how to use if and took some notes that I converted here to some more extensive documentation. Some things are pretty obvious, but the idea if to allow people to clearly see what bangsh can do for them. Let me know what you think!
Actually, you don't need to copy this task. You can simply run `/path/to/bangsh/bin/bang test` inside your project's root path. If you put that path in your `PATH` env var, you can simply run `bang test`.

```bash
$ exprot PATH="$PATH:/path/to/bang.sh/bin/"
$ cd my_project/
$ bang test
```

It must work, if it does not, we should fix it.