chapter goals

[m-clark]

Maybe there is enough with the intro/key-ideas, but should we add a 'goals' section at the beginning? For example, for lm chap

Chapter goals:

• Understand what a model is conceptually
• Understand what a linear model is and how features are mapped to the target
• Be able to get predictions from our model
• Be able to understand the results of a model at a basic level
• Get a sense of complexity and other issues

[m-clark]

Related: add quick summary of 'what was learned'.

[m-clark]

I'm leaving this for a future version, but won't incorporate now as I think there is plenty of text pdf-wise already.