Provide instructions for first-timers in readme

[HBehrens]

Right now, the readme is not very helpful for first-timers. This tasks describes the effort to improve this. @tyhoff had ideas such as providing example calls and to talk about -fstack-usage.

[g-berthiaume]

FYI: This post gives a brief introduction to the tool.

That being said, I also liked to see a better readme. As a windows10 user, I'm not sure how to use the --arm_tools_dir flag.