Hello Capella Community !
Please take note that we just have released a Gendoc version specially for you
This version is available there :
https://www.eclipse.org/gendoc/downloads/download.php
http://download.eclipse.org/gendoc/updates/releases/0.5.1-ju no/
This version is equivalent to Gendoc 0.5.1 but contains Sirius plugins to generate Capella Diagrams.
With this version all the instructions listed by Charlotte at the top of this post works with no problems at installation.
Please don’t hesitate to ask questions if you have some troubles