Updated installation docs for CRUX as a Docker Host.

Docker-DCO-1.1-Signed-off-by: James Mills <prologic@shortcircuit.net.au> (github: therealprologic)
Merge pull request #6006 from therealprologic/master

Updated installation docs for CRUX as a Docker Host.
Some fixes to the Intro pages

Docker-DCO-1.1-Signed-off-by: James Turnbull <james@lovedthanlost.net> (github: jamtur01)
Merge pull request #6001 from jamtur01/introfixes

Some fixes to the Intro pages
Adding User Guide

* Added User Guide sections.
* Moved HTTPS example to articles.
* Replaced Hello World example with User Guide.
* Moved use cases out of examples.

Docker-DCO-1.1-Signed-off-by: James Turnbull <james@lovedthanlost.net> (github: jamtur01)
Added new user guide sections

* Added Docker.io section
* Added Dockerized section
* Added Using Docker section

Docker-DCO-1.1-Signed-off-by: James Turnbull <james@lovedthanlost.net> (github: jamtur01)