Docs: Increase user of screenshots within our documentation

[joepavitt]

Description

Our docs are very text heavy, and include a lot of instructions around using the FlowFuse platform, but miss any screenshots. This can be difficult to maintain long term, but the text-heavy structure and content gives the impression of these tasks being difficult/technical to do. Showing off our UI can lighten the expectation of the user, and be more encouraging for them to use particular features.