simpleperf: update document about app profiling.

1. Remove instructions using command lines. Because I think it's easier
   to understand by focusing on script interface.
2. Remove texts that already exists in references, replace them with links.

Bug: http://b/69128787
Test: none.
Change-Id: Ia331673cf2e9fd10354d1ec5dc7857f3bb5e74da
1 file changed