[code-reflection] Integrated: Some documentation updates

[Gary Frost]

Updated docs to reflect reality.

Mostly additions describing project ideas. 

Added a section in the building/running with HAT, so how how we use `HAT` env variable to inject tracing, logging information at runtime.

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Commit messages:
 - Some documentation updates

Changes: https://git.openjdk.org/babylon/pull/497/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=497&range=00
  Stats: 465 lines in 4 files changed: 458 ins; 3 del; 4 mod
  Patch: https://git.openjdk.org/babylon/pull/497.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/497/head:pull/497

PR: https://git.openjdk.org/babylon/pull/497