DEVDOC: Add life of a gfxtrace (#579)
DEVDOC: Add life of a gfxtrace (#579)

Give an overview of how AGI captures and replays graphics API
commands. This can help developers build a mental model to navigate
the code.

Bug: n/a
google/agi,google/agi,google/agi,google/agi,google/agi,google/agi,google/agi,google/agi