Make the commands print a short usage summary and add a README file that
explains the dependencies.
Change-Id: I0c3f0713749ecfca23afaa2b536ac70dbdd7db0a
Reviewed-on: https://boringssl-review.googlesource.com/2471
Reviewed-by: Adam Langley <agl@google.com>
Initial fork from f2d678e6e89b6508147086610e985d4e8416e867 (1.0.2 beta).
(This change contains substantial changes from the original and
effectively starts a new history.)
