Merge "simpleperf: add doc for getting boot-time profile." am: 5cf73b1ea2 am: 47c4293e2f am: 84f9998106 am: 2b66969f26

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

Change-Id: I0290add2cbdf0146ea71d30396d1feaf38d2bfdd