chapter-4/2-similarity-search-level-2.ipynb Annoy section never loaded index after initializing, inaccurate performance measure

```
u = AnnoyIndex(2048)
%timeit u.get_nns_by_vector(feature_list[random_image_index], 5, include_distances=True)
```
The above code appeared a few times.
`u.load('data/caltech101index.ann')` is missing. Without it all returned indexes are empty. Performance measures are for an empty index, and are inaccurate (faster compared to with index loaded) by 10x on my CPU.