Documentation fixes and init_env bugs

Hi Vitaly,

The last five commits fix some errors in the documentation, and give a bit more details on how to use init_env.

There is also a commit fixing a bug in init_env itself. I'm not sure where this comes from... but on my machine init_env's --select-process or --select-process-userspace are broken (won't create any forks), whereas --select-process-code works with the change in the commit.

Have there been any relevant changes to the codeselector? Would you like to have a look?

Cheers,
Jonas