doc/requests: add internal links to make navigation easier
doc/requests: add link to job description docs
doc/requests: expand a little on what a ZeroVM image is
doc/requests: drop unnecessary quotes

In this context, "root" is not a literal.
doc/requests: make it explicit that the POST data is the script
doc/requests: rephase what a shebang line is
doc/request: add real link to Configuration.md