Typo in readme

The build instructions include the command:

```
git clone -recursive https://github.com/GModal/vSwell
```

This does not work. It should be:

```
git clone --recursive https://github.com/GModal/vSwell
```

Also, 

```
Open a terminal (or cd to) the ChaffVerb directory, then enter:
```

Should say to change to the `vSwell` directory.