Add section on harm weighting

[mpjashby]

At the moment, when asked to choose crime types for police to focus on, many (most?) students simply choose the most frequent. Add a section to explain on what basis you can choose to prioritise different types of crime, including joining harm weights to crime counts and then producing a harm-weighted bar chart.

[mpjashby]

This requires crime data for a location with (a) specific-enough crime categories for weighting and (b) an existing list of weights. I don't know of any publicly available data that has this, so at the moment this can't be implemented.