Small typos in documentation section "Taking Advantage of Spl"

**Describe the bug**
In section "Taking Advantage of Spl" the example
```
// Get the true realpath
echo $file->getRealpath();
```

contains two typos and should be replaced by
```
// Get the true real path
echo $file->getRealPath();
```

**CodeIgniter 4 version**
CodeIgniter4 Alpha 2 ff

