infra: Add led usage examples to README.md
infra: Add led usage examples to README.md

BUG=None
TEST=./tools/health-check

Change-Id: If6aa2de1e0ca1f5eda9de57fe4242b1a2bfe37d3
Reviewed-on: https://chromium-review.googlesource.com/c/crosvm/crosvm/+/3887352
Commit-Queue: Dennis Kempin <cd09796fb571bec2782819dbfd33307f65b1c778@google.com>
Reviewed-by: Zihan Chen <610a84a32f2086cdab4679002a95cbb619b0396d@google.com>

google/crosvm,google/crosvm,google/crosvm,google/crosvm