Merge "Document the tracing subscriber usage in README.md, better sample init" into main am: ca36a936b3 am: a14b14c067 am: 23be3df47c am: 6575b35a92

Original change: https://android-review.googlesource.com/c/platform/system/extras/+/2753571

Change-Id: If933dec1b23eb97516cda83dad57b30399050899
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>