Architecture Page: Improve Clarity

Intergrate feedback from @tacurran with previous revisions to architecture page, improving clarity, correcting typos, adding links, and improving formatting.

Signed-off-by: Dominic Serio <dominic@flynn.io>
We currently use "apps" exclusively (not "services") to describe applications/services in Layer 1. Happy to adjust that vocabulary, we just need to be very consistent.