RFR: CODETOOLS-7903279: doc updates

[Jonathan Gibbons]

Please review some updates to the FAQ and command-line help to address some recent suggestions for docs updates

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Commit messages:
 - add updated file
 - CODETOOLS-7903279: doc updates

Changes: https://git.openjdk.org/jtreg/pull/109/files
 Webrev: https://webrevs.openjdk.org/?repo=jtreg&pr=109&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903279
  Stats: 63 lines in 3 files changed: 56 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/jtreg/pull/109.diff
  Fetch: git fetch https://git.openjdk.org/jtreg pull/109/head:pull/109

PR: https://git.openjdk.org/jtreg/pull/109