R2.5: more discussion of finding implications / how to use them

[jessexknight]

Whilst recognising this is a scoping review, some more discussion on the impact of these findings for the global HIV response would be welcome. As noted in the discussion, modelled estimates "did not always reflect the available data". The key population estimates (and subsequent estimates of averted HIV transmission) are reliant on weak data and some informed comment on how these results should be used would be good.