document the difference in behavior in code completion between selecting items with tab or enter

```dart
class Thing {
int firstOne;
int secondOne;
Thing(this.secondOne);
}
```

Place your cursor between 'Thing(' and 'this' i.e. `Thing([CURSOR]this.secondOne)` Type `this.`, press `Tab` and notice how you end up with:

` Thing(this.firstOne.secondOne);` instead of `Thing(this.firstOne[CURSOR]this.secondOne);`

Or maybe even better would be `Thing(this.firstOne, [CURSOR]this.secondOne);` since it should be able to tell what I'm doing. :)

@pq told me to start filing these cases where IntelliJ autocomplete unexpectedly eats things after my cursor.

I feel like I'm used to other auto-complete systems never affecting anything after my cursor, but maybe I'm remembering wrong?