Update apt-get dependencies

* Also, tweak different sections to be consistent with the
  new quickstart.
* Squashed contributions by Jeremy (@bneg)
* add note about authors.rst
add include to testing howto too
Fixes to environment.rst. Closes: #4185
add prompt indication for the virtualenv
add pip install
Merge remote-tracking branch 'kali/feature/quickstart-and-deps' into develop