add ftrace tracing description into tutorial

Signed-off-by: Jovi Zhangwei <jovi.zhangwei@gmail.com>
Merge branch 'master' into android-4.4-integration

Update integration branch from https://github.com/ktap/ktap.git

* master:
  add ftrace tracing description into tutorial

Signed-off-by: Bryan Hundven <bryanhundven@gmail.com>