Add a readme with instructions on running tests

# Running Settings Robolectric tests

## The full suite

```

$ croot

$ make RunSettingsRoboTests

```

## Running a single test class

```

$ croot

$ make RunSettingsRoboTests ROBOTEST_FILTER=<ClassName>

```

For example:

```

make RunSettingsRoboTests ROBOTEST_FILTER=CodeInspectionTest

```

You can also use partial class name in ROBOTEST_FILTER. If the partial class name matches

multiple file names, all of them will be executed.