Update instructions in README

The README contained out-of-date examples of how to run things in OSv.
Fixed those.

BTW, Much of the contents of the README don't really belong there. We already
have separate documents for debugging in OSv, and how to compile C/C++
code for OSv, and these should probably be in documentation/ in the
git repository, instead of in a Wiki or Google docs.

Signed-off-by: Nadav Har'El <nyh@cloudius-systems.com>