Add TODOs/placeholders for essential diagrams and schematics

[bhs]

Ideally these TODOs would include a few words about what these diagrams are meant to explain or illuminate.

I am glad we started with the ideas+text, but this will be about 10x more accessible with a handful of well-executed schematic illustrations.

[austinlparker]

In lieu of me just plopping a bunch of TODOs in the files, can we hash out some ideas for it in this thread? I'm not sure what areas would benefit the most, but I'll drop some suggestions here:

Ch02

• This intro could use some sort of overarching illustration of the relationship between the concepts/principals
• Illustrations/diagrams of the different telemetry types here would make sense
• Illustrations/diagrams of resource telemetry would be useful?

Ch03

• Each subhead could use an illustration, but it could maybe be a single illustration at the top that demonstrated the layers and what was 'in' each of them. We could build on it in later chapters

Ch04

• This feels like it could use a diagram, but I'm not sure what.

Ch05 - 07

• I think we could re-use the 03 illustration here and focus in on individual components/parts of it?
• 05: Something to illustrate the dashboard metaphor here would be good imo.
• 06: Something to illustrate query-driven vs. workflow-driven investigation would be good?

Ch08

• This whole chapter is ripe for illustrations but I'm not sure what they should be. Off the top of my head, the sampling/aggregation sections could use some. I would like more feedback on the actual content here as well because I'm less confident about it than some earlier chapters.

Would also appreciate thoughts from @tedsuo and @bhs or whoever on specific suggestions/locations.