Merge "simpleperf: add doc for getting boot-time profile." am: 5cf73b1ea2 am: 47c4293e2f am: 84f9998106

Original change: https://android-review.googlesource.com/c/platform/system/extras/+/1961859

Change-Id: I33d16be7d6bbdab1e95f66310517701b18b57836