RFR: gc+regions needs to be at trace, not debug

[William Kemper]

Readme instructions have incorrect log level

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Commit messages:
 - gc+regions needs to be at trace, not debug

Changes: https://git.openjdk.org/shenandoah-visualizer/pull/2/files
  Webrev: https://webrevs.openjdk.org/?repo=shenandoah-visualizer&pr=2&range=00
  Stats: 3 lines in 1 file changed: 1 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/shenandoah-visualizer/pull/2.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-visualizer.git pull/2/head:pull/2

PR: https://git.openjdk.org/shenandoah-visualizer/pull/2