Error in README example

```
X = lparray.create_anon("Board", (3, 3, 3, 3, 9), 0, 1, pp.LpBinary)
```

Does not run, needs to be:

```
X = lparray.create_anon("Board", (3, 3, 3, 3, 9), cat=pp.LpBinary)`
```