Add a note to `ch14/1.question-answering-visualizer.ipynb` (and other notebooks in Chapter 14) that it requires that `outdoors` data set is already installed

[alexott]

We either need to add a comment, or add a code that will clone & unpack this dataset.

[alexott]

Also, do we need cells 8 & 9 there? It's just some calculations: 174/3 and 58/2